Method for lubricating treatment of aluminum

There are disclosed a method for lubricating treatment of an aluminum surface comprising subjecting the surface of aluminum or aluminum alloy to chemical zinc deposition plating, then to a treatment with a phosphating solution and further to a lubricating treatment, and a method for lubricating treatment of an aluminum surface comprising subjecting the surface of aluminum or aluminum alloy to chemical zinc deposition plating in a thickness of 0.2 .mu.m or more and further to a soap lubricating treatment.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for forming a lubricating film on 
a surface of aluminum or aluminum alloy (hereinafter abbreviated as 
"aluminum etc.") at the time of subjecting said aluminum etc. to cold 
forging, drawing and the like. 
Phosphate film is widely used as a lubricating film in cold forging or such 
of steel and nonferrous metals. 
Formation of phosphate film on aluminum etc. has so far been performed by 
using, for example, a solution of the following composition: Zn.sup.2+ 
:0.7%, PO.sub.4.sup.3- :1.0%, NO.sub.3.sup.- :2.0%, BF.sub.4.sup.- :1.0%. 
However, when aluminum etc. are treated with this solution, the situation 
of film formation changes in a short period, so that it has been difficult 
to form a desired phosphate film in a stable manner. In order to form the 
phosphate film stably it has so far been practiced to renew the solution 
frequently. However, the disposal of the waste liquor of the solution, 
which contains fluorides, is troublesome. 
An object of the present invention is to provide a method for stably 
forming a lubricating film suited to cold forging or such on aluminum etc. 
without the need of frequent renewal of treating solution. Further, the 
present invention discloses a method for forming a lubricating film on 
aluminum etc. by using a treating solution whose waste liquor can be 
easily disposed. 
The present inventors have made extensive study to find the reason why the 
situation of phosphate film formation changes in a short period as 
described above in the previous method of lubricating treatment, and as a 
result have made the following findings. 
i) When aluminum etc. are treated in a phosphating solution containing no 
fluoride the metal surface is coated by inactive oxide film or hydrated 
oxide film, which makes the formation of phosphate film largely 
impossible. 
ii) When a fluoride is incorporated into the solution, the inactive oxide 
film and hydrated oxide film are activated by a fluoride and the film 
layer of phosphate is formed. At this time, however Al.sup.3+ ions 
dissolve out into the treating solution and remain therein. 
iii) The Al.sup.3+ ions are gradually accumulated in the phosphating 
solution and come to inhibit the formation of phosphate film. Therefore, 
the solution containing accumulated Al.sup.3+ ions can hardly reproduce 
the situation of phosphate film formation as desired even when the 
concentrations of the other ingredients are adjusted by replenishment of 
chemicals. 
As described above, a treating solution containing a fluoride is naturally 
used in order to form phosphate film directly on the surface of aluminum 
etc. However, with the treating solution containing a fluoride, the 
situation of phosphate film formation becomes unstable in a short period. 
The present inventors have made further study on the method for forming 
phosphate film layer on aluminum etc. and as a resultantly attained the 
following findings. 
iv) When aluminum etc. are subjected beforehand to chemical zinc deposition 
plating, phosphate film layer can be formed stably on the aluminum etc. 
irrespective of whether the phosphating solution contains fluorine or not. 
v) When chemical zinc deposition plating is applied beforehand, no 
dissolution nor accumulation of Al.sup.3+ ions in the solution takes 
place, and the situation of phosphate film formation is maintained as 
desired in a stable manner even when the solution is repeatedly used over 
a long period. 
SUMMARY OF THE INVENTION 
The present invention has been achieved on the basis of the above findings. 
According to the first present invention, there is provided a method for 
lubricating treatment of an aluminum surface comprising subjecting the 
surface of aluminum of aluminum alloy to chemical zinc deposition plating, 
then to a treatment with a phosphating solution and further to a 
lubricating treatment. 
According to the second present invention, further, there is provided a 
method for lubricating treatment of an aluminum surface comprising 
subjecting the surface of aluminum or aluminum alloy to chemical zinc 
deposition plating in a thickness of 0.2 .mu.m or more and then to a soap 
lubricating treatment. 
DETAILED DESCRIPTION OF THE INVENTION 
The term "aluminum or aluminum alloy" used in the first and second present 
inventions refers to pure aluminum and aluminum alloys comprising aluminum 
as the main component, which include, for example, pure aluminum including 
1S and 2S, corrosion resisting aluminum-magnesium base alloys including 
52S and 56S, aluminum-manganese base alloys including 3S, 
aluminum-magnesium alloys including 61S and 63S, duralumins including 14S, 
17S and 24S, and extra super duralumins including 74S and 75S. The present 
invention may be applied to any of the various kinds of aluminum etc. 
mentioned above. 
In the first step of the methods of the first and second present 
inventions, the surface of aluminum etc. is subjected to chemical zinc 
deposition plating. The "chemical zinc deposition plating" referred to in 
the present invention means the zinc plating attained by the so-called 
zincate process, wherein aluminum etc. are immersed, for example, in an 
alkaline sodium zincate solution. For example, when aluminum etc. whose 
surface has been degreased and cleaned are immersed in a solution 
containing 52 g/l of Na.sub.2 O and 200 g/l of ZnO dissolved therein at 
room temperature for about 1 minute, a thin zinc plating layer of about 
0.5 .mu.m thickness is formed on the surface of aluminum etc. Since the 
zinc plating layer thus formed is very thin, it has hardly any function of 
protecting the aluminum surface, and has not been used previously as a 
lubricating film for aluminum etc. Thus far, chemical zinc deposition 
plating has been widely used as an undercoat plating when plating of other 
metals, e.g. nickel or copper, is applied onto aluminum etc. After the 
surface of aluminum etc., has been coated with a zinc layer of uniform 
thickness of about 0.1 .mu.m, the rate of zinc deposition becomes slow. 
Though a thicker zinc plating can be formed further, the resulting zinc 
layer tends to become spongy with non-uniform thickness. In a later step 
of the present invention, a zinc phosphate film is further formed on the 
zinc plating layer. If the zinc layer is spongy at the time, the adhesion 
of the zinc phosphate film becomes poor. Accordingly, in the first present 
invention, a zinc layer of a uniform thickness of about 0.1 .mu.m is 
preferred. Such a zinc layer can be easily formed as described above. 
Though the chemical zinc deposition plating of the present invention was 
explained with reference to a solution containing 52 g/l of Na.sub.2 O and 
200 g/l of ZnO as an example, the chemical zinc deposition plating layer 
used in the present invention may be formed also by other methods. For 
example, Japanese Patent Application Kokoku (Post-Exam. Publn.) No. 
40-6721, which relates to a zinc deposition plating used as an undercoat 
for a metal plating, uses a solution containing 100-700 g/l of an alkali 
metal hydroxide, 10-200 g/l of zinc oxide, and 1-200 g/l of an alkali 
metal gluconate. Also by this method, a zinc plating layer suited to 
forming a zinc phosphate film can be obtained. 
As described above, the chemical zinc deposition plating layer used in the 
present invention can be easily formed by various methods known to the 
art. Accordingly, the present invention is not particularly limited to the 
method of forming a chemical zinc deposition plating layer. 
In the second step of the method of the first present invention, the 
aluminum etc., subjected to chemical zinc deposition plating are further 
subjected to phosphating. The phosphating solution used in this step may 
be, for example, those which are used in forming zinc phosphate film on 
the surface of steel, e.g., an aqueous phosphating solution containing 
6-10 g/l of Zn.sup.2+, 10-20 g/l of PO.sub.4.sup.3- and 3-50 g/l of 
NO.sub.3.sup.- as the main components and optionally containing 1-5 g/l 
of Ca.sup.2+ and 0.05-0.5 g/l of Ni. As described before, when aluminum 
etc. are immersed in a zinc phosphate treatment solution containing no 
fluorine compound, no zinc phosphate film can be formed. In the first 
present invention, aluminum etc. coated by a chemical zinc deposition 
plating layer are, for example, immersed in a phosphating solution. In the 
present invention, therefore, the phosphating solution comes into contact 
not with aluminum etc., but with the chemical zinc deposition plating 
layer, so that a phosphate film is formed on the chemical zinc deposition 
plating layer. Through said second step, a phosphate film having a 
sufficient thickness as a lubricating film is formed on the surface of 
aluminum etc., through the medium of the chemical zinc deposition plating 
layer. The phosphate film thus formed shows a good adhesion to aluminum 
etc., and functions as a good lubricating film for cold forging and 
drawing. 
As described above, a conventionally used phosphating solution is employed 
in the first present invention. Further, the phosphating solution does not 
directly contact and react with aluminum etc. According to the method of 
the present invention, therefore, no dissolution nor accumulation of 
Al.sup.3+ ions in the phosphating solution takes place to change the 
situation of phosphate film formation, and a desired phosphate film can be 
formed stably. In the present invention, further, the conditions for film 
formation can be stabilized as desired over a long period of time by 
adjusting the composition of the phosphating solution through 
replenishment of chemicals without causing gradual accumulation of 
Al.sup.3+ ions in the phosphating solution or causing inhibition of 
phosphate film formation by accumulated Al.sup.3+ ions, so that frequent 
renewal of the solution is unnecessary. Further, phosphating solutions 
containing no fluorine may also be used in the first present invention, so 
that the disposal of waste liquid and waste water can be greatly 
simplified. 
In the third step of the method of the first present invention, a 
lubricating treatment is applied to aluminum etc., having phosphate film 
formed thereon. In cold forging and drawing, various lubricating 
treatments are applied after a phosphate film has been formed, which 
include a treatment of immersion in a soap solution followed by drying, a 
treatment of coating soap powders, and coating of lubricating oil. The 
lubricating treatment serves to lower the frictional resistance between 
the working tool and the work piece, thereby to facilitate the working and 
lengthen the life of the tool. The aluminum etc. having phosphate film 
formed thereon according to the present invention can be processed by 
various lubricating treatments known to the art. Such lubricating 
treatments provide the same effect as that obtainable by the prior art 
methods. 
According to the second present invention, chemical zinc deposition plating 
is applied onto aluminum etc., in a thickness of 0.2 .mu.m or more and 
then a soap lubricating treatment is applied directly onto the chemical 
zinc deposition plating layer without application of a phosphating 
treatment. 
The present inventors have applied chemical zinc deposition platings of 
varied thicknesses onto aluminum etc., then applied a soap lubricating 
treatment directly thereonto without application of a phosphating 
treatment, and examined the lubricating of the treated surfaces in cold 
forging and drawing. As a result it has been found that when the chemical 
zinc deposition plating layer has a thickness of less than 0.2 .mu.m the 
lubricity is insufficient, causing the seizure of the metal with tools 
etc., whereas when a chemical zinc deposition plating layer 0.2 .mu.m or 
more in thickness is formed, it will, coupled with soap lubrication, give 
an excellent lubricating film. 
Forming a chemical zinc deposition plating in a thickness of 0.2 .mu.m or 
more on aluminum etc., may be performed, for example, by the following 
method. Usually a chemical zinc deposition plating layer of a thickness of 
0.2 .mu.m or more has a porous surface. In the second present invention, 
however, even when the surface of the zinc plating layer is porous, it 
will given an excellent lubricating film when a soap lubricating treatment 
is applied to the zinc plating layer. Japanese Patent Application Kokoku 
(Post-Exam. Publn.) No. 60-15702 relates to a method of chemical zinc 
deposition plating for improving the corrosion resistance of aluminum 
etc., and discloses a method for forming a dense and thick zinc plating 
layer. Said patent application relates to a method for forming a 
nonporous, dense plating layer and teaches nothing of the technique of 
utilizing the zinc deposition plating layer as a lubricating film in cold 
forging etc. However, the dense film thus obtained also forms an excellent 
lubricating film when soap lubrication is applied thereto. The soaps which 
may be used in the soap lubrication may be those of alkaline or alkaline 
earth metals, sodium soaps being particularly preferred. 
According to the finding of the present inventors, these chemical zinc 
deposition plating layers show a good adhesion to aluminum etc., and give, 
those having a porous surface in particular, a lubricating film suited to 
cold forging and drawing when subjected further to a soap lubricating 
treatment.

PREFERRED EMBODIMENTS 
Example 
Phosphate films were formed on pure aluminum bars (50 mm in diameter and 
1,000 mm in length) according to the following process steps. In Nos. 1 
and 2 of Table 1, which refer to comparative examples using conventional 
methods, the pure aluminum base were immersed in a 30 g/l solution of Fine 
Cleaner #315 (a trade name of a weakly alkaline cleaner, mfd. by Nihon 
Parkerizing Co., Ltd.) at 70.degree. C. for 10 minutes, then washed, 
immersed in a phosphating solution containing a fluoride at 100.degree. C. 
for 5 minutes, and washed with water. In No. 1, the phosphating solution 
used was that immediately after renewal and had a low concentration of 
Al.sup.3+, enabling a phosphate film to be formed by immersion of 5 
minutes. In No 2, the phosphating solution used was that which had been 
used to form phosphate film on 1,000 pure aluminum bars mentioned above 
with 1 m.sup.3 of the solution and then whose concentrations of Zn.sup.2+, 
PO.sub.4.sup.3-, NO.sub.3.sup.- and BF.sub.4.sup.- were adjusted by 
replenishment of chemicals. 
TABLE 1 
__________________________________________________________________________ 
Chemical Lubricating 
zinc treatment 
deposition 
Phosphating solution 
Formation of 
sodium 
Lubricating 
thickness 
composition (wt %) phosphate 
soap base 
in cold 
No. 
(.mu.m) 
Zn.sup.2+ 
PO.sub.4.sup.3- 
NO.sub.3.sup.- 
BF.sub.4.sup.- 
Al.sup.3+ 
film*.sup.1) 
(g/l) working*.sup.2) 
__________________________________________________________________________ 
Comparative 
1 None 0.7 1.0 2.0 1.0 0 .largecircle. 
70 .largecircle. 
example 
Comparative 
2 None 0.7 1.0 2.0 1.0 0.05 
X 70 X 
example 
Example in 
3 0.1 0.7 1.0 2.0 -- 0 .largecircle. 
70 .largecircle. 
the first 
present 
invention 
Example in 
4 0.1 0.7 1.0 2.0 -- 0 .largecircle. 
70 .largecircle. 
the first 
present 
invention 
Comparative 
5 0.1 -- -- -- -- -- -- 70 X 
example 
Example in 
6 0.2 -- -- -- -- -- -- 70 .largecircle. 
the second 
present 
invention 
__________________________________________________________________________ 
Note 
*.sup.1) Good (Dark gray), X: Poor (color of the original material) 
(Judged by visual observation of the surface) 
*.sup.2) Good, X: Poor 
As can be seen from Table 1, since the treating solution of No. 2 contained 
accumulated Al.sup.3+ ions, a satisfactory phosphate film could not be 
formed with immersion of 5 minutes. Therefore, the treating solution of 
No. 2 must be renewed to obtain a satisfactory result, but since the 
treating solution contains a fluoride the disposal of the waste liquor is 
complicated. 
In Nos. 3 and 4, which refer to examples according to the first aspect of 
the present invention, the pure aluminum bars were immersed in a 30 g/l 
solution of Fine Cleaner #315 at 70.degree. C. for 10 minutes, then 
washed, and a chemical zinc deposition plating was applied thereto by 
immersing the bars in a 250 g/l Pre Coat T (mfd. by Nihon Parkerizing Co., 
Ltd., NaOH:25%, Zn.sup.2+ :5%) solution at room temperature for 10 
minutes, whereby a zinc plating layer of about 0.1 .mu.m thickness was 
formed. The aluminum base subjected to the chemical zinc deposition 
plating were washed with water and further immersed in a phosphating 
solution for 5 minutes. The phosphating solution used in No. 3 was that 
immediately after renewal. The phosphating solution used in No. 4 was that 
which had been used to form phosphate film on 1,000 pure aluminum bars 
with 1 m.sup.3 of the solution and then whose composition was adjusted by 
replenishment of chemicals. According to the method of the present 
invention, as can be seen in No. 4 of Table 1, the phosphating solution 
contains no Al.sup.3+ ion even after used for forming phosphate film on a 
large quantity of aluminum, and could form phosphate film under the same 
conditions as in No. 3 of Table 1, wherein a solution immediately after 
renewal was used. 
In No. 5 of Table 1, which refers to a comparative example, the same 
chemical zinc deposition plating as that in No. 3 of Table 1 was applied 
but the succeeding phosphating treatment was omitted and only a zinc 
plating layer of about 0.1 .mu.m thickness was formed on the aluminum bar 
surface. In No. 6 of Table 1, which refers to an example of the second 
present invention, a thick zinc plating layer of 0.2 .mu.m thickness was 
formed according to the method described before relating to the second 
present invention, and the phosphating treatment was not applied 
thereafter. 
In Nos. 1 to 6 of Table 1, the aluminum bars, after subjected to a soap 
lubricating treatment, were worked into bars of 42 mm diameter by drawing. 
The soap lubricating treatment was performed by immersing the bar in a 70 
g/l solution of UBE #235 (the trade name of a lubricant containing 
sodium soap as the main component, mfd. by Nihon Parkerizing Co., Ltd.) at 
80.degree. C. for 5 minutes. The results of examination of lubricating in 
the drawing operation are shown in Table 1. 
As can be seen from Table 1, in Nos. 3, 4 and 6, which refer to the method 
of the present invention, the same excellent lubricity is exhibited as in 
No. 1, which refers to the prior art method. On the other hand, seizure of 
the material with the tool occurred and the surface of the material was 
wounded in No. 2 of a comparative example owing to insufficient formation 
of phosphate film, and in No. 5 of a comparative example because the 
lubricating film was a thin zinc plating layer. 
According to the present invention, a lubricating film suited to cold 
forging and drawing can be formed stably at all times on the surface of 
aluminum etc. Further, according to the present invention, the solution 
used for forming the lubricating film can be employed over a long period 
without the need of frequent renewal. According to the present invention, 
since a lubricating film forming solution containing no fluoride can also 
be used, the waste liquid disposal and the waste water disposal can be 
performed in a simple manner.