Abstract:
Disclosed in an Al-based alloy for use as sliding material, superior in fatigue resistance and anti-seizure property consisting, by weight, of 1-10% Zn, 1-15% Si, 0.1-5% Cu, 0.1-5% Pb, 0.005-0.5% Sr, and the balance Al and incidental impurities.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an Al-based alloy for use as sliding material, superior in fatigue resistance and anti-seizure property. More particularly, the invention concerns an Al-based alloy for use as sliding material, superior in fatigue resistance and anti-seizure property, which is applied for half bearings of slide bearings, cylinder bushes, flanged bearings, thrust washers, etc., and which is suitable for applications in a wide industrial field including vehicles and industrial machines in particular equipped with high-load bearings. 
     STATEMENT OF THE RELATED ART 
     The prior art techniques which relate to this invention includes ones which are disclosed in, for example, West-German Patent Nos. 1,533,413 and 1,5578,696, the Specification of U.S. Pat. No. 4,170,469, and the Specification of British Patent No. 1,593,006. These disclosures are each concerned with Al-based alloys for use as materials of bearings, each alloy consisting, by weight, of 0.1-10% Zn, 0.1-20% Si, 0.1-10% Cu, and 0.1-10% Pb as essential components, 0.1-7% of at least one component selected, as an optional additive, from the group consisting of Ni, Bi and Mg, and the balance Al. 
     Internal combustion engines, mainly for automobiles have in recent years been rapidly advanced and have tendency to be further increased in speed and load applied. Therefore, even when the above-mentioned prior art Al-based alloys for use as sliding material are employed as the materials of bearings for higherspeed internal combustion engines in particular, the film of a lubricating oil comes to be thinned. Consequently, there has occurred a drawback that they are inferior in fatigue resistance as well as anti-seizure property. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of this invention is to provide an Al-based alloy for use as sliding material, which is superior in both fatigue resistance and anti-seizure property, thus eliminating the drawbacks inherent in the conventional Al-based alloys for use as sliding material. 
     The Al-based alloys which can attain the above object are the following four types of Al-based alloys: 
     (1) An Al-based alloy for use as sliding material, superior in both fatigue resistance and anti-seizure property consisting, by weight, of 1-10% Zn, 1-15% Si, 0.1-5% Cu, 0.1-5% Pb, 0.005-0.5% Sr, and the balance Al and incidental impurities. 
     (2) An Al-based alloy for use as sliding material, superior in both fatigue resistance and anti-seizure property consisting, by weight, of 1-10% Zn, 1-15% Si, 0.1-5% Cu, 0.1-5% Pb, 0.005-0.5% Sr, 0.05-5% in total of at least one component selected from the group A consisting of 0.05-5% Mg and 0.05-5% Ni, and the balance Al and incidental impurities. 
     (3) An Al-based alloy for use as sliding material, superior in both fatigue resistance and anti-seizure property consisting, by weight, of 1-10% Zn, 1-15% Si, 0.1-5% Cu, 0.1-5% Pb and 0.005-0.5% Sr, 0.05-2% in total of at least one components selected from the group B consisting of 0.05-2% Mn, 0.05-2% V, 0.05-2% Cr, and the balance Al and incidental impurities. 
     (4) An Al-based alloy for use as sliding material, superior in both fatigue resistance and anti-seizure property consisting, by weight, of 1-10% Zn, 1-15%Si, 0.1-5% Cu, 0.1-5% Pb and 0.005-0.5% Sr, 0.05-5% in total of at least one component selected from the group A consisting of 0.05-5% Mg and 0.05-5% Ni, 0.05-2% in total of at least one component selected from the group B consisting of 0.05-2% Mn, 0.05-2% V and 0.05-2% Cr, the total contents of said groups A and B being in a range of 0.05 to 4% and the balance Al and incidental impurities. 
     Next, the reasons for restricting the components of each Al-based alloy for use as sliding material, superior in fatigue resistance and anti-seizure property according to this invention, to the ranges described in Claims (1) to (4) (the reasons for determining the upper and lower limits of the content of each said alloy component) will be explained below together with the function thereof. 
     (1) Si: 1 to 15 wt % 
     (a) When fine grains of Si having high hardness (about 600 Hv) are dotted in the matrix of Al, only the Al matrix having a soft surface is worn. Consequently, the surface of the alloy is in the form of irregularities as viewed microscopically. Thus, the convex silicon grains resist a high load with their non-adhesion property being maintained as it stands while the concave portions play the role as of oil reservoirs. Thus, the alloy has resistance to high load, to thin oil film, and further to contact with metal. 
     (b) The Si grains which are finely dotted serve to abrade edges, burrs, etc. of the surface of the mating shaft so as to improve the anti-seizure property. In this case, when the Si grains are coarse, there is the risk of their locally overabrading the shaft as well as of their being taken away. This requires control or limitation of their size. 
     (c) When metallic contact is instantaneously made between the Al matrix and the mating shaft, seizure and fluidity of the alloy bearing are prevented because of non-adhesion property of silicon in the alloy surface and the non-flowability of the Al matrix having Si as the core thereof. 
     (d) Where the content of silicon is less than 1%, the alloy fails to exhibit wear resistance as well as the advantageous properties shown in the above items (a), (b) and (c). Where the content of silicon exceeds 15%, the alloy becomes brittle, inferior in strength against impact fatigue, and deficient in toughness, so that the alloy is low in plastic workability at the time of production such as rolling, extruding, etc. 
     Preferably, the silicon content is in the range of 3 to 8 wt %. 
     (2) Zn: 1 to 10 wt % 
     (a) Zn is in solid-solution state in the Al matrix to thereby vary the lattice spacings thereof, so that a the adhesion property thereof is reduced. 
     (b) Zn is preferentially oxidized in comparison with aluminum to obviate the harmness of a hard Al oxide film. 
     (c) Zn acts to increase the compatibility of the alloy with lubricating oil. 
     (d) Where the content of zinc is less than 1 wt %, the alloy becomes inferior in wear resistance as well as in anti-seizure property. Where the content of zinc exceeds 10 wt %, there occurs such a risk that the alloy bearing is apt to cause a stress corrosion cracking, and at the same time becomes inferior in toughness. Besides, in a case where soft material such as an overlay is applied onto the surface of the alloy, there occurs difficulty in making adhesion of, for example, an electric plating layer. Besides, in this case, there occur adverse influence on bondability obtained by roll-bonding. 
     Preferably, the zinc content is in the range of 2 to 8 wt %. 
     (3) Cu: 0.1 to 5 wt % 
     (a) The addition of Cu increases the strength of Al matrix, and is very effective in raising the fatigue resistance. However, if the alloy becomes too high in hardness, a problem arises in respect of compatibility. the same thing applies to Ni as well. 
     (b) If the content of Cu is less than 0.1%, no significant advantage is brought about by Cu. Where the content of Cu exceeds 5%, the alloy becomes excessively high in hardness with the result that the compatibility decreases and the toughness also decreases. 
     Preferably, the Cu content is in the range of 0.5 to 2 wt %. 
     (4) Pb: 0.1 to 5 wt % 
     The addition of Pb improves the machinability as well as the anti-seizure property of the alloy. However, where the content of Pb is less than 0.1 wt %, no significant effect is obtained by the addition of Pb. Where the content of Pb is above 5 wt %, it becomes very difficult to obtain uniform dispersion of Pb into the Al matrix, and the strength of the alloy is influenced adversely. 
     Preferably, Pb content is between 0.5 wt % and 3 wt %. 
     (5) Sr: 0.005 to 0.5 wt % 
     (a) Sr serves to finely crystallize the grains of silicon. 
     (b) Sr improves the mechanical property, particularly the elongation of the alloy. 
     (c) In a case where Sr is less than 0.005 wt %, no significant advantage is brought about by addition of Sr. In a case where Sr is more than 0.5 wt %, the ductility of the alloy decreases. 
     Preferably, Sr content is between 0.01 wt % and 0.1 wt %. 
     (6) Mg and/or Ni selected from the group A: 0.05 to 5 wt % 
     (a) Mg and/or Ni is in solid-solution state in Al matrix, or is precipitated in the form of intermetallic compound, thereby increasing the fatigue strength thereof. 
     (b) In a case where Mg and/or Ni is less than 0.05 wt %, no substantial effect is obtained by addition of Mg and/or Ni. In a case where Mg and/or Ni is more than 5 wt %, the alloy becomes excessively high in hardness, so that it becomes inferior in the compatibility, and the toughness of the alloy decreases. 
     Preferably, the content of Mg and/or Ni is 0.1 wt % to 3 wt %. 
     (7) At least one component selected from the group B consisting of Mn, V and Cr: 0.05 to 2 wt % 
     (a) The component or components are in solidsolution state in Al matrix, or are precipitated in the form of intermetallic compounds, thereby improving the mechanical property of the alloy under high temperature. And, 
     (b) Where the content of the component or components is less than 0.05 wt %, no substantial advantage is obtained by addition thereof. In a case of more than 2 wt %, the grains of the intermetallic compounds become coarse in size with the result that the alloy becomes brittle. 
     (8) the total content of the components selected from the groups A and B: 0.05 to 4 wt % 
     (a) The components are in solid-solution state in Al matrix, or are precipitated in the form of intermetallic compounds, thereby improving the resistance to fatigue. 
     (b) Where the total content is less than 0.05 wt %, no substantial effect is obtained. Where the total content exceeds 4 wt %, the alloy becomes too high in hardness, so that the alloy becomes inferior in the compatibility and the toughness thereof also decreases. 
     Preferably, the total content thereof ranges between 0.1 wt % and 3 wt %. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a table showing the results of a fatigue test concerning respective composite bearings of the prior art and this invention; 
     FIGS. 2(a) and 2(b) are block diagrams showing basic processes for manufacturing composite bearings according to this invention, respectively; and 
     FIG. 3 is a sectional view of a part of a composite bearing which view is depicted from a photograph of microstructure of the composite bearing produced by a preferred embodiment of this invention, the photograph being taken with a magnification of 100. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 3, the reference numeral 1 indicates a steel backing layer, 2 being a bearing alloy layer, 3 being an intermediate layer, and 4 being an overlay. 
     The product of this invention will now be described in detail by way of the following Examples while compared with conventional products. 
     EXAMPLE 1 
     Alloys Nos. 16 to 30 according to this invention and comparative alloys Nos. 1 to 15, both being shown in Table 2, were each cast at a temperature of 750° C. to 850° C. into rods having a diameter of 10 inches. After each of the rods had been annealed at a temperature of 400° C. to 500° C., it was extruded into a sheet at the extrusion ratio of 35 to 45. This sheet was annealed at a temperature of 350° C. to 450° C. and then was rolled to a rolled member. Thereafter, the rolled member was annealed at a temperature of 300° C. to 400° C. and then was roll-bonded under pressure onto a steel backing at the reduction rate of 30 to 50%, thus obtaining a bimetal member. This bimetal member was annealed at a temperature of 300° C. to 400° C. and then was plastically worked into a semi-circular shape. This semi-circularly plastically worked member was plated, on its inner surface, with a Pb-10% Sn alloy having a thickness of 10 to 20 microns to provide an overlay. Thus, a semi-circular composite bearing was obtained. The process of manufacturing this composite bearing is shown in FIG. 2(a) while a section of a part of the composite bearing is shown in FIG. 3. 
     The fatigue test and seizure test were conducted under the conditions shown in Table 1 regarding said semi-circular composite bearings, the results of the former test being shown in FIG. 1 while the results of the latter test are shown in Table 3 each sample being tested three times. 
     Further, the bimetal members prior to the plastic working into the semi-circular shape were tested regarding their mechanical properties, the results being shown in Table 2. Among these mechanical properties, the adhesion strength was tested in the following manner. Namely, bimetal members each having a width of B (mm) were prepared. Then, there were formed two parallel grooves with an interval of L mm on the bimetal member, one of which grooves extends from the outer surfaces of the bearing alloy layer to the interface of the bonding, another of which grooves extendeds from the outer surface of the steel backing to the interface of the bonding. Then, respective ends of the two test pieces at the opposite sides were pulled in opposite direction. Then, the pulling load as measured when the steel backing layer was peeled off from the bearing alloy layer was divided by an bonding area of B×L (mm 2 ) to determine the bonding strength. 
     EXAMPLE 2 
     Bimetal members each having the same shape as in Example 1 were prepared and composite bearings each having the same shape as in Example 1 were prepared from said bimetal members, in the process of FIG. 2(b), under the same conditions, and using the same alloy, as in Example 1 of which the process steps are shown in FIG. 2(a), with the exception that, instead of the extrusion and the annealing after the extrusion shown in FIG. 2(a), there were used a rolling step and an annealing of 300° C. to 400° C., respectively. the same tests as in Example 1 were conducted regarding the bimetal members and composite bearings thus prepared, the results being substantially the same as in Example 1. 
     In Examples 1 and 2 and with reference to FIG. 3, an intermediate Ni-plated layer having a thickness of 1.5 microns was provided between the bearing alloy layer 2 and the overlay 4 in order to obtain bonding strength therebetween. This intermediate layer 3 may be also provided by using Cu or a Cu alloy in lieu of Ni. Further, in Examples 1 and 2, the steel backing layer 1 and the bearing alloy layer 2 were directly pressure-bonded to each other. It is well known, however, that mutual pressure bonding of both the layers 1 and 2 with a Ni plating or Al foil interposed therebetween improves the bonding strength to a larger extent. 
     This invention has the following excellent advantages. 
     (A) The alloy of this invention has improved fatigue resistance and anti-seizure property as compared with the conventional alloys (see FIG. 1 and Table 3) 
     (B) In the bearing properties, anti-seizure (non-fluidity and non-adhesion) property in particular is remarkably improved because of the respective actions of Al matrix in which Zn is in solid-solution state, Si finely crystallized and dispersed by addition of Sr, and Pb dispersed in Al matrix. And, 
     (C) In view, particularly, of the fact that, since, coarse, Si grains cause damages to the mating shaft when in use, the size of Si crystal grains is limited to 15 microns or less by adding a small amount of Sr in the case of the present invention. Thus, it is possible to improve the anti-seizure property to a larger extent than in the case of conventional alloys. 
     
                       TABLE 1A______________________________________Conditions For The TestFatigue Test______________________________________Test Method Soda Type Dynamic Load Test MethodNumber Of   4000 r.p.m.RotationsTesting Time       20 HrPeriodCircumferen-       13 m/sectial SpeedOil-Feeding 120° C.TemperatureOil-Feeding 3 kg/cm.sup.2PressureLubricating SAE 20OilAngle At    Advanced Angle: 36°Which OilIs FedEvaluation  &#34;Fatigue&#34; is deemed to have occurredMethod For  when fatigue has occurred in regard toFatigue     the bearing area of not less than 5%______________________________________ 
    
     
                       TABLE 1B______________________________________Conditions For TestSeizer Test______________________________________Test Method  Sapphire Test MethodNumber Of    3250 r.p.m.RotationsCircumferen- 9.0 m/sectial SpeedOil-Feeding  90 to 95° C.TemperatureOil-Feeding  4.5 kg/cm.sup.2PressureAmount Of Oil        20 cc/minTo Be FedOil Clearance        0.04 to 0.06 mmLubricating  SAE 20OilMethod Of    After idle operation of 15 min. under noApplying Load        load, the motor is run for 10 min. under        a load of 700 kgf/cm.sup.2. Thereafter, the        load is stepwise increased 70 kgf/cm.sup.2        for each 10-minute passage (up to 1610        kgf/cm.sup.2)Method Of    &#34;Seizure&#34; is deemed to have occurredDeciding The when the temperature of rear surface ofTime Of      the bearing has increased to 200° C. orSeizure      more, or when the motor has beenOccurrence   overloaded.______________________________________ 
    
     
                                           TABLE 2__________________________________________________________________________                                 Mechanical Property                                 Tensile                                      Elon-                                          Bonding                                               Hard-Type ofSample    Chemical Composition of Bearing Alloy (wt %)                                 Strength                                      gation                                          Strength                                               ness                                                   StructureSampleNo. Al   Si           Zn             Cu               Pb                 Sr Mg Ni                         Mn V  Cr                                 kgf/mm.sup.2                                      %   kg/mm.sup.2                                               Hv 5                                                   of__________________________________________________________________________                                                   BearingPrior1   balance         1 10             3 1 -- -- --                         -- -- --                                 26   15  8.0  62  Steel Back-Art  2   &#34;    1 8 2 0.3                 -- -- --                         -- -- --                                 24   16  8.5  60  ing Layer +3   &#34;    2 8 1 4 -- -- --                         -- 0.15                               --                                 23   16  8.5  59  Bearing Al-4   &#34;    2 7 0.5               1.5                 -- -- 1 -- 1  --                                 23   19  8.5  55  loy Layer +5   &#34;    3 4 1 1 -- -- --                         -- -- --                                 18   27  10.0 45  Overlayer6   &#34;    3 6 5 1.5                 -- -- --                         -- -- --                                 26   9   9.0  64  (Surface7   &#34;    4 6 1.5               3 -- -- 0.1                         -- 1.5                               1 24   11  9.5  61  Layer)8   &#34;    4 5 1.5               0.5                 -- 4  --                         1  -- --                                 23   17  10.0 62  The over-9   &#34;    6 5 2 2 -- 1  --                         1.5                            -- 0.1                                 24   18  9.5  64  layer con-10  &#34;    6 4 1.2               1 -- 0.5                       --                         -- -- --                                 19   20  10.0 56  sist of 10%11  &#34;    6 4 0.8               0.5                 -- 0.1                       4 0.1                            0.1                               1.5                                 29   10  9.5  65  Sn and 90%12  &#34;    8 3 0.5               5 -- -- --                         -- -- --                                 23   14  9.0  63  Pb.13  &#34;    10           2 0.2               3 -- -- --                         -- -- --                                 27   10  9.0  6414  &#34;    13           1 0.2               2 -- -- --                         -- -- --                                 29   8   9.5  6515  &#34;    15           1 0.1               0.1                 -- -- --                         -- -- --                                 29   6   9.5  64The  16  &#34;    1 10             3 1 0.008                    -- --                         -- -- --                                 25   16  8.5  63Present17  &#34;    1 8 2 0.3                 0.01                    -- --                         -- -- --                                 25   16  8.5  58Invention18  &#34;    2 8 1 4 0.01                    -- --                         -- 0.15                               --                                 21   18  9.0  5819  &#34;    2 7 0.5               1.5                 0.04                    -- 1 -- 1  --                                 23   20  8.5  5320  &#34;    3 4 1 1 0.04                    -- --                         -- -- --                                 16   28  9.5  4321  &#34;    3 6 5 1.5                 0.1                    -- --                         -- -- --                                 28   8   10.5 6122  &#34;    4 6 1.5               3 0.2                    -- 0.1                         -- 1.5                               1 23   11  9.0  6223  &#34;    4 5 1.5               0.5                 0.2                    4  --                         1  -- --                                 21   16  9.5  6224  &#34;    6 5 2 2 0.05                    1  --                         1.5                            -- 0.1                                 25   18  10.0 6325  &#34;    6 4 1.2               1 0.04                    0.5                       --                         -- -- --                                 20   21  10.5 5526  &#34;    6 4 0.8               0.5                 0.1                    0.1                       4 0.1                            0.1                               1.5                                 28   12  10.0 6427  &#34;    8 3 0.5               5 0.2                    -- --                         -- -- --                                 24   15  9.5  6328  &#34;    10           2 0.2               3 0.2                    -- --                         -- -- --                                 26   11  9.0  6529  &#34;    13           1 0.2               2 0.3                    -- --                         -- -- --                                 28   8   10.0 6430  &#34;    15           1 0.1               0.1                 0.5                    -- --                         -- -- --                                 29   7   9.0  63__________________________________________________________________________ 
    
     
                       TABLE 3______________________________________Maximum Load Just Before SeizureType of  Sample  Seizure Load of Bearing (kgf/cm.sup.2)Sample No.     1120 1190 1260 1330                        1400 1470 1540 1610______________________________________Prior  1                          o    ooArt    2                          o    oo  3                          o    o    o  4                          o    oo  5                               o    oo  6                          o    oo  7                               oo   o  8                               oo   o  9                          o    o    o  10                              oo   o  11                    o    oo  12                         o         oo  13                              o    oo  14                              oo   o  15                         o    o    oThe    16                              oooPresent  17                              oo   oInvention  18                              oo   o  19                              oo   o  20                                   ooo  21                              o    oo  22                                   ooo  23                              o    oo  24                              o    oo  25                              o    oo  26                              oo   o  27                                   ooo  28                                   ooo  29                                   ooo  30                              o    oo______________________________________ each o represents a test result