Hollow charge

An improved process for metallurgically bonding two layers of metal capable of forming brittle intermetallics, by means of propelling one of the layers progressively into collision along the other layer at a velocity and impact angle selected to produce a waveless, complete metal to metal bond substantially free of the formation of brittle intermetallics along the entire interfacial region of contact between said layers; and includes the welded product formed thereby.

FIELD OF INVENTION 
This invention relates to an improved method for the metallurgical bonding 
of metals capable of forming brittle intermetallics by propelling one 
layer progressively into collison along another layer, and particularly 
relates to the application of explosion welding procedures for welding 
layers of metal which form brittle intermetallics. 
More particularly, this invention relates to the fabrication of improved 
welded products, the bond being substantially free of intermetallics by 
utilizing the improved method for the metallurgical bonding of metals 
where brittle intermetallics could form. 
BACKGROUND TO THE INVENTION 
Solid phase welding is a method of welding metals by the application of 
pressure so as to produce interfacial plastic deformation of the metals at 
the interfacial surfaces which breaks up the contaminant surface films to 
expose virgin contact surfaces for bonding. 
A solid phase weld may be achieved by a process identified as "impact 
welding" which consists of driving or propelling one metal layer against 
another metal layer at a sufficient velocity and at an oblique impact so 
as to cause bonding of the two metal layers together at the common 
interfacial region of contact. Impact Welding has been achieved by those 
skilled in the art by utilizing magnetic propulsion equipment, gas guns 
and explosives to propel the metal layers together. If the metals are 
driven together by means of explosion, the process is known as explosion 
welding. 
In explosion welding, metal plates or layers which are to be welded are 
spaced apart relative to one another in either generally parallel relation 
or inclined relation, and a layer of suitable explosive charge disposed on 
one of the metal layers is detonated so as to impart kinetic energy to the 
"flyer" plate causing the flyer plate to collide obliquely with the 
stationary "parent" plate. The explosive while detonating produces a force 
normal to the flyer plate causing the flyer plate to impact the parent 
plate obliquely at a collision or impact angle. As the detonation proceeds 
along the flyer plate, it progressively drives the flyer plate along the 
parent plate at a particular welding velocity. If two metal layers are to 
be bonded the explosive charge may be disposed on both metal layers. 
U.S. Pat. Nos. 3,728,780 and 3,137,937 generally relate to explosion 
welding, which may be utilized to weld different metals together. 
U.S. Pat. No. 3,813,758 teaches that a metal jet is formed at the point of 
impact between the flyer plate and parent plate. It is believed that this 
jet which contains the contaminant surface layers of both plates is forced 
outwardly at a high velocity during the explosion welding process. This 
cleaning operation allows a solid phase weld to be formed between the 
interfacial virginally clean metallic surfaces of the plates under the 
intense local pressure in the region of contact. 
U.S. Pat. No. 3,583,062 discloses that three types of bonded zones may 
result from explosion welding, namely: 
(a) a direct metal to metal bond (with a straight interface); 
(b) a uniform melted layer in which the metals are bonded together with an 
intervening layer of solidified melt of substantially homogeneous 
composition; 
(c) a wavy type of bond zone comprised of periodically spaced discreet 
regions of solidified melt, between areas of direct metal to metal bond. 
Moreover, U.S. Pat. No. 3,397,444 generally teaches that products having 
the wavy type bond interface are preferred in many situations because of 
their normally higher strength, and defines values of parameters such as 
collision velocity so as to produce the preferred wavy interface. 
Similarly, U.S. Pat. No. 3,583,062 states that the wavy bond zone is 
preferred over the substantially straight bond because of the larger 
interfacial area the wavy bond provides, and also defines the value of 
certain parameters which will produce the preferred wavy interface. 
However for metal combinations tending to form brittle intermetallics, the 
melt associated with the bonded wavy interface presents zones of weakness. 
Metal combinations which tend to form brittle combinations are well known 
to those skilled in the art and generally encompass those metal 
combinations which have a wide dissimilarity between the densities of the 
metals to be bonded, which include for example, aluminum to steel, 
zirconium to steel , tantalum to steel, titanium to steel, titanium to 
copper, and their respective alloys. 
Brittle intermetallics are diffusion products, and are undesirable, 
particularly when the welded zone is subjected to an increase in 
temperature which enhances diffusion. 
Diffusion may be defined as a transfer of atoms into the vacancies and 
interstitial spaces from one metal to another; and diffusion is enhanced 
with an increase in temperature in the region of interfacial contact. In 
particular diffusion is enhanced in the region of pockets of melt 
associated with the bonded wavy interface as, during the welding process, 
these regions are subjected to elevated temperatures, due to the adiabatic 
rise of same at the vortex of each wave. Moreover, for the wavy morphology 
to occur, the entire interface has to be subjected to a higher energy than 
that necessary for a straight interface which will consequently produce 
larger plastic deformation and hence higher temperatures, further 
enhancing diffusion. 
Furthermore, mechanical solicitation (such as dynamic or static bending) 
applied to a wavy interface causes the weld to fail in metal combinations 
capable of forming brittle intermetallics, as the interfacial pockets of 
melt create zones of weakness. 
Efforts have been made to retard the diffusion process in the bonded zone 
particularly for those metal combinations capable of forming brittle 
intermetallics and particularly when such metal combinations are exposed 
to an elevated temperature, by utilizing diffusion barriers. In the case 
of aluminum to steel such barriers are titanium, nickel, chromium, 
molibdenum, silver, etc., or ferritic stainless steel as disclosed in 
Canadian Pat. No. 917,869, which are sandwiched between and 
metallurgically bonded between the flyer and parent plate. However, the 
use of such barriers increases the cost of the explosion welded product, 
and their efficiency is quite relative. 
OBJECTS OF THE INVENTION 
The principle object of this invention is to provide improvements in 
metallurgically bonding metal layers capable of forming brittle 
intermetallics wherein the metal layers are driven together for solid 
phase welding in the region of interfacial contact so as to produce welds 
having superior strength characteristics. 
More particularly, it is an object to provide an improved method for 
welding metals by impact welding and explosion welding. 
A further important object resides in providing an improved welded product 
without the need of diffusion barrier interlayers. 
SUMMARY OF INVENTION 
In accordance with one aspect of this invention there is provided a process 
for metallurgically bonding at least two layers of metal capable of 
forming brittle intermetallics, by propelling one of the layers 
progressively into collision along the other layers the improvement 
comprising, selecting the velocity and impact angle so as to produce a 
substantially waveless, complete metal to metal bond substantially free of 
the formation of brittle intermetallics along the entire interfacial 
region of contact between the layers. The metal layers may be selected 
from the group comprising steel, stainless steel, aluminum, copper, 
tantalum, nickel, titanium, zirconium, gold, silver, platinum, columbian, 
molybdenum, magnesium, chromium, tungsten, palladium, zinc, and their 
respective alloys. 
Another aspect of this invention resides in a method of welding at least 
two metal layers together along a common interfacial region of contact 
wherein the metal layers are characterized as capable of forming brittle 
intermetallics, by positioning the layers in generally spaced apart 
relation, applying a layer of explosive charge along the outer surface of 
one or both of the layers remote from the other layer, and detonating the 
explosive charge so as to weld the plates together, the improvement which 
comprises, selecting both the strength of explosive charge and the spacing 
between the layers so as to propel one of the layers progressively into 
collision along the other layer at a velocity and impact angle selected to 
produce a substantially waveless,complete metal to metal bond 
substantially free of the formation of brittle intermetallics along the 
entire interfacial metallurgical bond. A layer of protective material or 
buffer may be applied to the outer surfaces of one of the layers remote 
from the other layer and then applying the layer of explosive charge upon 
the buffer. In one embodiment, the layers are positioned generally 
parallel to one another while in another embodiment the layers are 
positioned in inclined relation to one another. 
Still more particularly, it is an aspect of this invention to provide a 
method for metallurgically bonding two metal layers along a common 
interfacial region of contact, wherein the metal layers are characterized 
as capable of forming brittle intermetallics the method comprising 
positioning the layers in generally spaced apart parallel relation, 
applying a protective material adjacent the outer surface of one or both 
of the layers remote from the other layer, applying a layer of explosive 
charge upon the protective material, and detonating the explosive charge 
so as to produce a welded bond, the improvement which comprises selecting 
both the strength of explosive charge and the spacing between the layers 
so as to propel one of the layers progressively into collision along the 
other layer at a velocity and impact angle selected to produce laminar 
flow of the metal layers at the interface during detonation of the 
explosive charge and produce a welded bond having a waveless, complete 
metal to metal interfacial bond substantially free of the formation of 
brittle intermetallics along the entire interfacial region of contact 
between said layers. 
Yet another aspect of this invention resides in a method of producing 
bonded metal layers capable of developing brittle intermetallics and 
having improved strength characteristics in spite of prolonged exposure to 
elevated temperatures, by propelling one of the layers against the other 
to obliquely impact the layers together at a velocity and impact angle 
selected to produce a substantially waveless interfacial bond between the 
layers. 
Another aspect of this invention resides in a welded product comprising two 
metal layers capable of forming brittle intermetallics, wherein the metal 
layers are metalurgically bonded by propelling the layers together, and 
having a substantially waveless interfacial bond along a common 
interfacial region of contact. 
A further aspect of this invention lies in a welded product comprising two 
metal layers capable of forming brittle intermetallics which have been 
metalurgically bonded by propelling the layers together, and having a 
substantially waveless interfacial bond with substantially no 
intermetallics along a common interfacial region of contact. 
A transitional joint for aluminum smelters comprising two metal layers 
capable of forming brittle intermetallics and metallurgically bonded so as 
to present a waveless complete metal and metal bond substantially free of 
the formation of brittle intermetallics along the entire interfacial 
region of contact between said layers.

DESCRIPTION OF INVENTION 
Explosion Welding 
Throughout the figures identical parts have been given identical numbers. 
FIG. 1 illustrates the inclined arrangement of explosion welding with the 
flyer plate 2 at an initial preset angle a between the flyer plate 2 and 
the parent plate 4, which arrangement is usually adopted when using a high 
detonation velocity explosive and/or small plates. 
FIG. 4 shows the parallel arrangement of explosion welding where the flyer 
plate 2 is initially positioned substantially parallel to and spaced apart 
from the parent plate 4 by a uniform stand-off d and which arrangement is 
usually adopted when using a low detonation velocity explosive and/or 
large plates. 
For both the inclined arrangement illustrated in FIG. 1 and the parallel 
arrangement illustrated in FIG. 4 a uniform layer of explosive charge 6 
covering the flyer plate 2 is detonated by the detonator 8 in a manner 
well known to those skilled in the art. A protective material or buffer 
10, such as rubber, polythene, cardboard or even a thick coat of plastic 
paint may be utilized to protect the top surface of the flyer plate 2 from 
damage. As can be observed from FIGS. 1 and 4 the parent plate 4 may rest 
on top of an anvil 12 to absorb the impact upon detonation of the 
explosive charge. The anvil 12 rests over a surface 14. 
The explosive charge 6 is detonated by the detonator 8 to impart kinetic 
energy to the flyer plate 2 causing it to collide obliquely against the 
parent plate 4 at a collision point S illustrated in FIG. 2 for the 
inclined arrangement and FIG. 5 in the parallel arrangement. 
The explosive charge 6 when detonated produces a pressure normal to the 
flyer plate imparting to it a velocity Vp illustrated in FIGS. 2 and 5 
respectively. 
The detonation of the explosive charge 6 proceeds along the flyer plate 2 
at a velocity Vd illustrated in FIGS. 2 and 5 respectively and drives the 
flyer plate 2 progressively into collision with the parent plate 4. Under 
these conditions, the collision point S travels along the parent plate at 
a velocity herein referred to as welding velocity Vw illustrated in FIGS. 
2 and 5 respectively. 
In the parallel arrangement shown in FIG. 5, the welding velocity Vw is 
equal to the detonation velocity Vd, and the flyer plate 2 impacts the 
parent plate 4 obliquely at a collision angle b. 
Relative to the collision point S, the flyer plate 2 appears to be moving 
with a velocity Vf towards the collision point S. 
FIGS. 3 and 6 illustrate the geometric configuration of the process 
variables describing the inclined and parallel arrangements respectively 
for welding metal plates together by explosion. 
From FIG. 3, the trigonometrical relationship between the detonation 
velocity Vd and the welding velocity Vw is obtained from triangle ASB as: 
##EQU1## 
Formula 1.1 is independent of the direction of the flyer plate impact 
velocity Vp and cannot be solved as it contains two unknowns b and Vw. The 
relationship between Vp, Vd and b which involves only one unknown b 
depends on the assumption regarding the direction of Vp. From FIG. 3, it 
is possible to deduce the following relationship: 
##EQU2## 
Various boundry conditions have been tentatively assumed, none of which are 
entirely satisfactory but which all appear to lead to somewhat similar 
results for small collison angles b. Accordingly, equation (1.2) can be 
applied to the following 5 cases which, when solved, enable the solution 
for equation (1.1). 
(a) The Normal To Vp Bisects a 
This implies the flyer plate is stretched during the process but recovers 
afterwards in such a way that AB=AB.sup.1. In this case: 
##EQU3## 
(b) The Normal To Vp Bisects b The flyer plate's length after stretching 
remains unchanged such that SB=SB.sup.1. 
##EQU4## 
(c) Direction of Vp Bisects SBC If the direction of Vp bisects SBC then: 
EQU Vp=2Vd sin ((b-a)/2) (1.5) 
(d) Direction of Vp is Normal to AB.sup.1 
##EQU5## 
(e) Direction of Vp is Normal to SB 
EQU Vp=Vd sin (b-a) (1.7) 
The above-identified equations were all derived from the inclined 
arrangement, but this does not effect the analysis for the parallel setup 
where a=o for equation (1.1) reduces to: 
EQU Vw=Vd (1.8) 
and equations (1.3) and (1.6) both reduce to: 
EQU Vp=Vw tan b (1.9) 
and equations (1.4) and (1.5) reduce to: 
EQU Vp=2Vw sin b/2 (1.10) 
and finally equation (1.7) reduces to: 
EQU Vp=Vw sin b (1.11) 
The Jetting Phenomenon 
It is believed that if the impact velocity Vp under oblique high velocity 
impact is sufficient and the collision angle b exceeds some minimum value, 
then a jet or spray 16 is formed at the collision point S as illustrated 
in FIG. 7. This jet 16 contains the contaminant surface layers of both 
plates 2 and 4 and is forced outwardly at a high velocity. Such removal of 
the contaminant surface layers allows a solid phase weld to be formed 
under the intense local pressure in the region of contact. This pressure 
is so great that the metal layers 2 and 4 in the region of collision 
behave for a short time as either nonviscous fluids or fluids of low 
viscosity. 
The Explosion Bonded Interface 
FIG. 8 is a diagram of a magnification of an explosive welded straight or 
plane interface between two metal layers 2 and 4. 
FIG. 9 is a diagram of a magnification of an explosion welded uniform 
melted layer 18 in which the metals of layers 2 and 4 are bonded together 
with an intervening layer of solidified melt 18 of substantially 
homogeneous composition. 
FIGS. 10 and 11 are diagrams of a magnification of an explosion welded wavy 
interface for similar and dissimilar density metals, respectively, 
comprised of periodically spaced discreet regions of solidified melt 20 
between areas of direct metal to metal bond 22. The solidified melt 20 is 
created as the temperature at the vortex of each wave rises adiabatically 
followed by an extremely rapid cooling due to the dissipation of heat at 
the bulk of the metals far away from the interface. 
It is believed that during such as dynamic process, the metals at their 
interface behave as fluids and that the characteristic interfaces 
illustrated in FIGS. 8 and 9 are examples of laminar and transition flow 
respectively and FIGS. 10 and 11 are examples of turbulent flow. 
The mechanism of wave formation has been the subject of detailed study and 
theorization for many years. According to the fluid-like analogy the 
mechanism of wave formation may be described as the formation of vortices 
during the turbulent flow of metals at the interface. However, other 
models have evolved, which all could be operative during the process. 
Presently those skilled in the art prefer the wavy interface, illustrated 
in FIGS. 10 and 11, in the belief that: 
(a) such a wavy interface increases the area of surface bonding thereby 
creating stronger bonds; 
(b) mechanical interlocking occurs between the two metal layers 2 and 4 
which has been defined as a zip-like effect. 
It has been found, however, that in accordance with the invention described 
herein superior welds are obtained for metal combinations capable of 
forming brittle intermetallics by producing a straight or waveless 
interfacial bond which contains either non-detectable or negligible 
diffusion zones, at the bonded interface, as illustrated in FIG. 8, rather 
than by the wavy bond illustrated in FIG. 11 (which corresponds to the 
interfacial morphology of dissimilar metal combinations) 
Welding Windows 
A method shall now be described for determining those values of welding 
velocity and impact angle for specific metal combinations which will 
produce a straight or waveless interfacial bond by impact welding. Such 
method shall be more fully described herein but generally involves the 
generation of data using many values of welding velocity and impact angles 
and observing the type of bond resulting therefrom. The results are then 
plotted on a graph identified as the "Welding Window" for that particular 
metal combination with the welding velocity plotted on the y co-ordinate 
and the impact angle on the x co-ordinate. 
A gas gun was utilized to generate the required data rather than an 
explosive because of the difficulties encountered in controlling and 
measuring the variables during the explosion welding process. However the 
data obtained from the gas gun are applicable to explosion welding. 
Only a general description of the equipment and operation of the gas gun 
shall follow. A more detailed discussion of the gas gun utilized herein 
may be found in the 1977 publication of The Queen's University of Belfast, 
Report No. 1080 entitled "The Design and Development of a 63.5 m.m. Bore 
Gas Gun for Oblique Impact Experiments and Preliminary Results by A. 
Szecket and B. Crossland. 
Gas Gun 
The similarity of the explosive welding process with the gas-gun is 
illustrated in FIG. 16. This similarity enables the usage of the gas-gun 
as a simulation system of explosive welding. 
The gas gun 30 illustrative in FIG. 12 was utilized to propel a flyer plate 
2 inside the barrel 32 of the gas gun against the parent plate 4. 
The gas gun 30 includes a pressure chamber or gas receiver 34, a bursting 
disc 36, a velocity measuring system 38 and support pad 54. 
A compressor system (not shown) is employed to deliver a gas under pressure 
to the pressure chamber 34 through conducts (not shown). The pressure 
chamber 34 is sealed at one end thereof by a bursting disc 36 which is 
shown in FIGS. 13, 14 and 15. 
As shown in FIGS. 13 and 14, the bursting disc 36 has two "V" crosscuts 44 
which are scribed along one face of the bursting disc 36 at an angle of 60 
degrees at various depths t. The bursting disc 36 is located between the 
pressure chamber 34 and barrel 32 and clamped into position. The bursting 
disc 36 is adapted to burst as illustrated in FIG. 15. 
Initially, the bursting discs 36 is capable of withstanding the pressure 
buildup in pressure chamber 34. However as the pressure of gas in the 
pressure chamber 34 reaches a critical value which depends on the material 
of the bursting disc 36 and the thickness of the scribe t, the bursting 
disc 36 ruptures which will release the pressurized gas into the barrel 
32. 
The flyer plate 2 in the gas gun is carried by a sabot 52 as shown in FIG. 
12. The sabot 52 is made of light-weight material and adapted to carry the 
flyer plate 2 by means of a double sided adhesive tape or adhesive. 
As the bursting disc 36 bursts, the pressure of the gas is released into 
the barrel 34 which propels or drives the sabot 52 with the flyer plate 2 
towards the parent plate 4, at an impact velocity Vp. By utilizing 
bursting disc 36 of different materials, thicknesses and different 
thicknesses of scribe t, the pressure at which the disc 36 bursts may be 
controlled; and hence the impact velocity Vp of the flyer plate 2 may be 
measured. 
The sabot 52 is completely destroyed upon impact of the flyer plate 2 with 
the parent plate 4. 
The parent plate 4 is held in an oblique mounting pad 54 is illustrated in 
FIG. 12. The mounting pad 54 is machined to give a particular value of 
angle of impact b. By using mounting pad 54 having different impact angles 
b, the angle of impact may be controlled. 
The velocity Vp of the sabot 52 is measured electronically by a variety of 
methods which are well known to those skilled in the art and will 
therefore not be described herein. 
By knowing the impact velocity Vp and the angle of impact b, it is possible 
to calculate the welding velocity Vw along the parent plate 4 in 
accordance with the formulas referred to earlier. This is possible because 
of the similarity of the welding process which occurs with the gas gun 30 
and explosion welding as illustrated in FIG. 16. 
The actual value of the welding velocity Vw may also be measured 
electronically by methods well known to those skilled in the art. 
The actual measured welding velocity Vw compared favourably with the 
calculated welding velocity Vw in accordance with the formulas outlined 
above. 
Material Utilized for Flyer and Parent Plate in the Gas Gun 
The gas-gun is a tool for the systematic study of the weldability between 
similar and dissimilar metals. The window described here corresponds to a 
particular metal combination. Accordingly, it should be understood that 
the gas-gun is not limited to that particular metal combination. 
The material utilized in the gas gun 30 for the flyer plate 2 and parent 
plate 4 was copper in two different thicknesses, namely 1.58 mm for the 
flyer plate 2 and 10 mm for the parent plate 4, both in the half hard 
condition. According to BS 899 which is the designation for the raw 
material and Bs 1036 (C101) which applies to an electrolitic tough pitch 
high conductivity copper, rolled according to BS 2870/4, the chemical 
composition for both thicknesses was as follows: 
______________________________________ 
Other Impurities 
Cu Pb Bi (excluding oxygen) 
______________________________________ 
99.9% 0.005% 0.001% 0.03% 
______________________________________ 
Operation of Gas Gun in Impact Welding Half Hard Copper to Half Hard Copper 
In Impact welding half hard copper to half hard copper, a range of angle 
support pads 54 were utilized in the gas gun 30. The angle of impact b was 
preset for the particular angle support pad 54 which was utilized in the 
gas gun. 
Similarly a range of bursting discs 36 of a particular metal and particular 
scribe thickness t were utilized to produce an impact velocity Vp of the 
flyer plate 2, and hence a particular welding velocity Vw along the parent 
plate 4. 
Flyer plate 2 and parent plate 4 were cut from their respective copper 
sheets and machined to size. The flyer plate 2 was machined to 38 by 36 by 
1.58 mm and the parent plate was machined to 40 by 40 by 10 mm. 
The surfaces of the flyer plate 2 and parent plate 4 to be impacted were 
prepared by thoroughly cleaning them with a 400 grade emergy paper and 
subsequently degreasing with acetone. 
The parent plate 4 was located in the support pad 54 by means of a quick 
curing araldite adhesive, while the flyer plate 2 was mounted centrally on 
the sabot 52 by a double sided tape. 
The sabot 52 was introduced into the barrel 34. 
The relative alignment of the flyer plate 2 and the parent plate 4 was 
accomplished by a thin strip of adhesion tape fixed diametrically across 
the back of the sabot 52. 
After locating the bursting discs 36, the gas gun 30 was assembled. 
After firing, the gun 30 the welded composite comprising of half hard 
copper flyer plate 2 welded to the half hard copper parent plate was 
removed from the gas gun. A visual inspection of the welded composite was 
carried out to see if a weld had occurred. If a weld occurred, the 
specimen was sectioned and subsequently it was faced on a central lathe. 
If the weld withstood these fairly severe machining operations, the 
specimen was polished, and etched in an alcoholic ferric chloride solution 
for metallurgical examination, and micrograph photography. 
The micrograph of the metal composite was examined to see and measure the 
weld morphology. This procedure was repeated for each welded composite 
produced with the different values of welding velocity impact angle, wave 
lengths, wave amplitudes or a straight interfacial bond evaluation. 
Results 
Each of the specimens were visually observed as described above and plotted 
on the graph illustrated in FIG. 17 in a manner which may be best 
described by referring to the following examples relating to the bonding 
of half hard copper to half hard copper. 
Example 1: 
By Impact welding with a welding velocity of 3,000 meters per second and 
impact angle of 10 degrees the micrograph of the resulting welded 
composite showed a wavy interface with front and rear vortex much like 
that illustrated in FIG. 10. 
Example 2: 
By impact welding, with a welding velocity of 2,000 meters per second and 
impact angle of 20 degrees the micrograph of the resulting welded 
composite showed a wavy interface much like the one illustrated in FIG. 
10. 
Example 3: 
By impact welding with a welding velocity of 1,500 meters per second and 
impact angle of 10 degrees the micrograph showed a straight waveless 
interface like the one illustrated in FIG. 8. 
Example 4: 
By impact welding with a welding velocity of 1,000 meters per second and 
impact angle of 20 degrees the micrograph of the resulting welded 
composite showed a straight waveless interfacial bond as illustrated in 
FIG. 8. 
Example 5: 
By impact welding with a welding velocity of 1,000 meters per second and 
impact angle of 25 degrees the micrograph of the resulting welded 
composite showed an interface which exhibited portions of irregular wavy 
interface and straight interface. 
Example 6: 
By impact welding with a welding velocity of 1,500 meters per second and 
impact angle of 25 degrees the micrograph of the resulting welded 
composite showed a wavy interface with a single vortex like that 
illustrated in FIG. 11. 
The results of the impact welding including the examples described above 
were plotted on a graph with welding velocity on the y axis and impact 
angle on the x axis. 
After plotting the results on the graph, it was possible to define; 
(a) zone A in which all of the specimens had a straight or waveless 
interface in the region of contact; 
(b) zone B in which irregular wave together with portions of straight bonds 
could be detected at the interface; 
(c) zone C in which all of the specimens had a wavy interface in the region 
of contact. However this region presents two different wave morphologies 
depending on the impact parameters, namely an interface like that 
illustrated in FIG. 10 with front and rear vortex which corresponds to 
similar density explosive welds and an interface like that illustrate in 
FIG. 11 with a single vortex which corresponds to dissimilar density 
explosive welds. 
Generally, specimens lying outside of the periphery P of the welding window 
had incomplete or no bonding between layers. More specifically, below the 
lower velocity boundary over the whole range of impact angles partial or 
poor bonds or no bonds were formed, the interface being characterized by 
trapped surface contaminants and the presence of voids particularly at 
lower values of b. The upper velocity limit was characterized by the 
presence of excessive melting. 
The welding window of FIG. 17 for half hard copper to half hard copper 
provides all of the interfacial geometries experienced in the explosive 
welding process. 
By controlling the welding velocity Vw and impact angle b to: 
(a) fall within the zone of plain interfacial weld, a straight or waveless 
interfacial bond is produced along the common interfacial region of 
contact between the plates; 
(b) fall in the transition zone, an interface having irregular waves 
together with portions of straight interface may be produced; and 
(c) fall within the zone of wavy interface, a wavy interface is produced 
along the common interfacial region of contact. 
Thickness of Flyer and Parent Plates in the Gas Gun 
As referred to earlier the thickness of the flyer plate and parent plate 
utilized in the gas gun was 1.58 mm and 10 mm respectively. If a thicker 
flyer plate is used the upper boundary illustrated in FIG. 17 would come 
down or in other words be displaced downwardly toward the x axis due to 
the creation of excessive melt as a result of the difficulty in 
dissipating heat with higher kinetic energies. On the other hand the right 
hand boundary illustrated in FIG. 17 would move closer to the y axis as 
this limit boundary is related to the rigidity of the flyer plate. The 
other boundaries in FIG. 17 would remain substantially constant. 
Accordingly the thickness of the plates utilized in the gas gun will have a 
bearing on the relative shape or boundary of the welding window plotted 
for a particular metal combination which is impact welded together. 
Different Metal Combinations 
Although FIG. 17 illustrates the welding window for the bonding of half 
hard copper to half hard copper, similar welding windows may be 
constructed for different metal combinations, when impact welding or 
explosion welding different metals of flyer plate 2 and parent plate 4. 
FIG. 27 illustrates metal combinations which have been successfully bonded 
by means of explosion, and accordingly welding windows may be developed 
for the metal combinations outlined in FIG. 27. 
The parameters of the impact welded or explosion welded joint may be 
controlled so as to select the angle of impact b between the flyer plate 2 
and parent plate 4 and to select the velocity Vw of progressively 
obliquely impacting the plates along each other so as to produce a 
waveless interfacial bond. 
For example, it has been found that a waveless interfacial bond is 
consistently produced between the explosion welding of aluminum 1100 to 
half hard copper by having: 
(a) a welding velocity Vm of 1,850 meters per second; and 
(b) an impact angle of 12 degrees. 
Furthermore, a waveless interfacial bond is consistently produced between 
the explosion welding of aluminum 1,100 to low carbon steel with up to 
0.20 percent carbon (i.e. up to AISI C1020 or equivalent) by having: 
(a) welding velocity Vw of 1,750 meters per second; and 
(b) an impact angle of 16 degrees. 
Moreover, a waveless interfacial bond is consistently produced between the 
explosion welding of half-hard copper to titanium 35 A by having: 
(a) a welding velocity of Vw of 2,200 meters per second; and 
(b) an impact angle of 11 degrees. 
The values for Vw and b given for the impact welding of aluminum 1100 to 
half hard copper, aluminum 1100 to low carbon steel, and half-hard copper 
to titanium to produce a waveless interfacial bond are not to be 
interpreted as limiting, as welding windows similar to FIG. 17 may be 
constructed for these metal combinations as well as for other metal 
combinations having a range of Vw and b falling within the zone of plane 
interface. Any value of Vw and b falling within the zone of plane 
interface will produce a bond having a waveless interface. 
It will be understood to those skilled in the art that in explosion 
welding, the welding velocity Vw and the impact angle may be controlled by 
employing a suitable explosive and selecting the stand-off between the 
plates. 
The waveless interfacial welded bond between: 
(a) aluminum 1100 to half hard copper; 
(b) aluminum 1100 to low carbon steel having up to 0.20 percent of carbon; 
(c) half-hard copper to titanium 35 A. 
contained no detectable diffusion zone and thus no detectable brittle 
intermetallic phases even though these metal combinations tend to form 
metastable phases. There was no detectable intermixing of aluminum to 
copper or aluminum to steel or copper to titanium respectively at the 
bonded interface, and thus no intermetallic formation could be delineated 
for the straight interfacial bond. 
The Straight Waveless Interface 
FIG. 21 is a diffusion profile of the relative concentrations of aluminum 
into steel and vice versa at various positions from the interface of a 
straight waveless explosion bond between aluminum and steel. FIG. 21 was 
prepared by focusing a micro beam on the interface and reading the 
relative compositions of aluminum and steel at various distances from the 
interfaces. The resulting graph shows a negligible amount of diffusion at 
the substantially straight waveless interfacial bond. 
Strength of Straight Waveless Interface 
Metal plates which tend to form brittle intermetallics in the bonded region 
and which metal plates have been bonded together by driving the flyer 
plate 2 against the parent plate 4 so as to produce a waveless interfacial 
bond in the region of contact exhibit superior strength characteristics 
over bonds exhibiting wavy interfaces upon bending of the plates 2 and 4 
about the bonded region as illustrated in FIGS. 18, 19 and 20. 
FIG. 18 illustrates bonding of two different metal layers 2 and 4 having a 
straight interface 90; namely aluminum for metal layer 2 and low carbon 
steel having up to 0.20 percent carbon steel for metal layer 4. The 
phantom lines in FIG. 18 illustrate the metal joint before bending. After 
bending, both statically and dynamically (such as heavily hammered), the 
metal layer 2 about the waveless interface at 90 degrees and 180 degrees 
as illustrated in FIGS. 18 and 19 respectively, the aluminum layer 2 
"stretches" without tearing about the straight interfacial bond. There was 
no separation at the interface although striations were observed on the 
surface of the aluminum. 
However, a static bend of less than 90 degrees applied to bonded metals 
having a wavy interface produces a discreet distribution of fractures 100 
of the interface at each vortex zone, as illustrated in FIG. 20. 
When the low carbon steel layer 4 contained an amount of carbon above 0.20 
percent carbon (i.e. above AISI C1020 or equivalent) a small amount of 
intermetallics became perceptible at X 400 magnification at the straight 
interfacial bond. However the welded product was still substantially 
better than the wave-like morphology as there was no tearing about the 
straight interfacial bond after subjecting the welded joint to a 90 degree 
and 180 degree bend (both static and dynamic) as illustrated in FIGS. 18 
and 19 respectively. 
The melt associated with the wavy interface present zones of weakness or 
inherent weld defects which fracture when subjected to bending and other 
excessive exterior solicitations. 
Hence, explosion welded joints having straight waveless interfaces have 
superior strength characteristics over wavy interfaces for metal 
combinations capable of developing brittle intermetallics. 
Straight Interfacial Bonds Exposed to Elevated Temperatures 
Metal plates characterized as tending to form brittle intermetallics and 
which have been bonded together by driving the flyer plate 2 against the 
parent plate 4 so as to produce a waveless or straight interfacial bond in 
the region of contact exhibit improved strength characteristics after 
prolonged exposure to service temperatures. For example the service 
temperature of an explosively welded aluminum to low carbon steel 
transition joint utilized in an aluminum reduction cell would be in the 
vicinity of about 300 to 400 degrees centigrade. 
Yet a bonded zone of aluminum 1,100 to low carbon steel (with up to 0.20 
percent carbon steel) having a waveless interface which was produced by: 
(a) selecting the welding velocity Vw at 1,750 meters per second; and 
(b) an impact angle of 16 degrees; was exposed to: 
(i) a temperature of 480 degrees C. for six hours and showed no detectable 
intermetallic formation; 
(ii) a temperature of 500 degrees C. for three hours and showed to 
detectable intermetallic formation; and 
(iii) a temperature of 520 degrees C. for three hours with no detectable 
intermetallic formation. 
By utilizing the invention described herein, aluminum to steel bonds are 
produced having a waveless interface with substantially no melt or 
intermetallics. Furthermore, there were no intermetallic formations which 
could be observed by subjecting the bonded aluminum to steel straight 
interface to the temperatures and length of time referred to above. It is 
believed that this occurs because of the absence of melt in the straight 
or waveless interface bond, and therefore the diffusion process which 
leads to intermetallics is retarded. 
Application of Impact Welded Joints 
The impact welded product having a straight interfacial bond has many 
industrial applications. For example: 
(a) titanium to steel, or aluminum to steel, or zircalloy to inconnel 
joints. The zircalloy to inconnel joint may be used in pressurized water 
reactors due to the favourable thermal neutron absorption cross-sections 
and high resistance to corrosion. 
(b) aluminum to stainless steel joints of tubes used in cryogenics. 
(c) in aluminum smelters, the anode and cathode are jointed to the electric 
bus bars by means of an aluminum to steel transition joint. 
WAVY VS STRAIGHT OR WAVELESS BOND 
For greater particularity, it is apparent to those persons skilled in the 
art that: 
(A) WAVY INTERFACE 
(i) the term Wavy Interface refers to the wavy interface generated in the 
direction parallel to the direction of detonation, 
(ii) a straight or waveless interface may be observable in a direction 
perpendicular to the direction of detonation, as illustrated in FIGS. 10 
and 11, although it is more likely that a wavy interface will be seen 
having a lower frequency than the frequency of the waves generated in the 
direction of detonation. 
(B) STRAIGHT OR WAVELESS INTERFACE 
(i) the term straight or waveless interface refers to the straight waveless 
interface generated in the direction parallel to the direction of 
detonation, 
(ii) a straight or waveless interface will also be observable in a 
direction perpendicular to the direction of detonation. 
STRAIGHT OR WAVELESS INTERFACE AND HOLLOW CHARGE 
It is well known that by hollowing an explosive charge and detonating same, 
the explosive force is converged onto a small area. By lining the hollow 
in the explosive charge with a metal liner, and detonating same, the 
explosive collapses the metallic liner into a slug and a high-speed metal 
jet which can perforate armor plate. Thus, the shaped charge phenomena has 
given rise to the development of a number of devastating weapons such as 
the bazooka. 
FIG. 22 shows in cross-section, a hollow charge 102 of cylindrical 
cross-section. The hollow charge 102 comprises of explosive charge 103, a 
detonator 101, a booster 99, a coned shaped hollow 104, and metal liner 
105. The coned shaped hollow 104 has an angle a between the axis of the 
cylinder and walls of the coned shaped metal liner 105. 
FIG. 23 shows the hollow charge 102 an instant following detonation. The 
detonation of the explosive 103 along the metal liner 105 drives the metal 
liner walls 105a and 105b progressively into collision with each other to 
form a metal jet 106 and a slug 107. 
It is evident that a similarity exists between the detonation of the hollow 
charge as depicted in FIG. 23 and the explosion welding as depicted in 
FIG. 2. However, the objective in the hollow charge is to maximize the 
metal jet 106, while the objective in explosive welding is to maximize the 
slug (which is the "product") and minimize the jet which serves only as a 
decontaminating mechanism. 
The linear collapse produces a continuous jet 106 with a velocity gradient. 
The tip of the jet 108 travels at a high velocity V.sub.TIP, and the 
velocity decreases toward the tail of the jet 109 with a velocity 
V.sub.TAIL. This velocity gradient causes the jet 106 to stretch until it 
breaks into segments 110 as shown in FIG. 24. The penetration capability 
decreases as the jet breaks. The distance between the tip 106 and the 
operator is called the stand-off. It is an object to maximize the 
stand-off up to the point where the tip begins to break. 
In one particular example of a hollow charge lined with copper, the tail 
velocity V.sub.TAIL may reach values of 3,000 meters/second while the tip 
velocity V.sub.TIP may reach values as high as 8-10 km/second. The 
stagnation pressure due to a V.sub.TIP of 8-10 km/second greatly exceed 
the ultimate tensile strength of conventional armor, and therefore, the 
metal jet 106 is capable of penetrating such armor. 
It is well known that the penetration capability of the metal jet 108 is 
proportional to the square root of the density of the metal liner 105. 
Therefore, heavy metals having relatively larger densities, such as gold 
or tantalum are found to be more effective. 
It is also known that only a minor part of the conical liner 105 actually 
contributes to the metal jet 106 and the attendant penetration process, 
while the remainder of the liner 105 forms the slug 107. 
Therefore, bi-metal liners have been produced, as shown in FIG. 25, whereby 
an inexpensive low-density metal 111, such as copper, is utilized for the 
rear side of the metal liner 105 in contact with the explosive, which will 
eventually form the slug; and a relatively expensive high-density metal 
112, such as tantalum, utilized in the front side for the eventual 
formation of the metal jet 106 for a more effective penetration. 
The bi-metal liners 105 have been only recently joined together, for 
example by: 
(a) mechanical clamping of metal liners 111-112, or 
(b) electro plating one of the layers 111 to the other layer 112. 
However, upon detonation of the hollow charge, reflection waves will appear 
due to the difference in the accoustic impedance between the joined metals 
111 and 112 which may cause destruction of the entire assembly, before the 
jet is formed. Both mechanical clamping or electroplating create poor 
attachment strengths. 
##EQU6## 
It has been found that an explosively welded bi-metal liner 105 between the 
low-density material 111 and the high-density material 112, gives an 
excellent attachment strength which withstands the stressing due to the 
above mentioned reflections. 
On the other hand, the coherency of the jet 106 is extremely sensitive with 
the surface finishing of the cone, or hemisphere. 
Moreover, there is a built-in instability which is characteristic of this 
phenomenon, that is a pulsating pressure 114 originating at the 
impact-point 113, which will eventually manifest itself by causing the 
breakage of the tip of the jet. It is believed that this instability is 
enhanced by the surface roughness; which means that the superficial 
asperites, voids, and microdefects behave under the explosive load as 
"microbazookas"; i.e. sources of microjetting which could deviate the main 
jet from its coherency. 
Prior to the invention described herein explosive welding was usually 
associated with a wavy interface between the two metal-layers. 
Thus, if the high density metal 112 while jetting encounters the wavy type 
bond, the aforementioned instability will be increased; thus limiting the 
stand-off. 
If the explosively welded interface between the low density metal 111 and 
the high density metal 112 is substantially waveless, the inherent 
instability generated by the system is minimized and thereby the stand-off 
could be increased. 
Parameters, such as welding velocity and impact angle, for producing 
explosion welded liners having substantially waveless interfacial bond, 
may be determined by the simulation system of the explosion welding 
process, namely, the gas gun which produces an impact weld, between any 
particular metal combination. 
The hollow charge 102 may have a metal liner 105 shaped like a cone as 
described in FIGS. 22 and 23, or any other shape such as a hemisphere as 
shown in FIG. 26. 
The hemispherical shape can be utilized to produce a metallic jet 106 
having substantially no slug 107. 
The metal liner 105 may be formed by explosive forming, in the manner well 
known to those in the art. 
The potential achievable range of velocities for V.sub.TIP and V.sub.TAIL 
for metal jets developed by conical liners and hemispherical liners are as 
follows: 
For the Conical Liner 
V.sub.TIP =7-10 km/second 
V.sub.TAIL =2-4 km/second 
For the Hemispherical Liner 
V.sub.TIP =4-6 km/second 
V.sub.TAIL =1.5-3 km/second 
The penetration characteristics of the hollow charge are a function of the 
ratio defined as: 
EQU V.sub.TIP /V.sub.TAIL 
The greater the ratio the better the penetration characteristics of the 
jet. In this regard, the penetration ratio may be increasd by either 
increasing V.sub.TIP or decreasing V.sub.TAIL, or both. 
By utilizing a hollow charge having a metal liner comprising of at least 
two metal layers which have been metallurgically bonded by explosion 
welding and having a substantially waveless interfacial bond therebetween, 
either the V.sub.TIP of the jet may be increased closer to the maximum 
potential achievable range as outlined above, or the V.sub.TAIL of the jet 
may be decreased closer to the minimum potential achievable range as 
outlined above, or both; thereby increasing the V.sub.TIP /V.sub.TAIL 
ratio, and improving the penetration capabilities of the hollow charge. 
Although the preferred embodiments as well as the operation and use have 
been spcifically described in relation to the Drawings, it should be 
understood that variations in the preferred embodiments could easily be 
achieved by a skilled man in the trade without departing from the spirit 
of the invention. Accordingly, the invention should not be understood to 
be limited to the exact form revealed in the Drawings.