US3531337A - Hard aluminum alloy - Google Patents

Description

United States Patent 3,531,337 HARD ALUMINUM ALLOY Ichiro Kawakatsu, 31 Yayoicho, Itabashi-ku, Tokyo, Japan No Drawing. Filed Dec. 26, 1967, Ser. No. 693,100 Claims priority, application Japan, Dec. 26, 1966, 41/ 84,560 Int. Cl. C22c 21/00 US. Cl. 14832.5 4 Claims ABSTRACT OF THE DISCLOSURE An aluminum alloy having high hardness and abrasion resistance elevated by subjecting an alloy containing 2.6- 7.8% zinc, and 0.6-3.8% magnesium as principal additive elements to 'be the principal aging hardeners, in addition thereto, O.21.2% of each of iron, nickel and cobalt of transition metal of Group IV, 0.11.2% manganese, 0.5% or below chromium, and at the same time containing ODS-1.2% zirconium (in some cases, replaced in part with titanium or hafnium) of Group IV, ODS-0.3% boron which is a metalloid, and 0.050.85% silicon and the remainder of aluminum to nitriding treatment while the alloy is molten state, and then to the solution treatment at a temperature 450490 C. as being cast or after worked, thereafter applying the aging hardening to the alloy at a temperature of 85 to 130 C. and in some cases, before the hardness reaches the maximum point in the aging treatment, further applying plastic work to the alloy.

The aluminum alloys which are widely used as construction materials are light in weight as well as considerably strong. However, the alloys have defects in actual use thereof in such points that their hardness are far lower than those of iron and steel materials or other nonferrous materials such as copper alloys, etc. Namely, when compared with other metallic materials, the aluminum alloys are relatively soft, and therefore the surfaces of the alloys are not only readily scratched, but also deformed or worn away. Accordingly they cannot be used as screw nuts, and other parts of machines.

Table 1 shows the comparison of hardness between typical constructional metals and practically used high tension aluminum alloys.

TABLE 1.-COMPAR1SON OF HARDNESS OF TYPICAL CONSTRUCTIONAL MATERIALS AND PRACTICALLY USED ALUMINUM ALLOYS As shown above, the hardness of high tension aluminum is in general limited to 120-135, while the hardness of copper alloys is much higher than this. The hardness of carbon steel becomes also considerably higher than this when it is subjected to heat treatment. Therefore, for the actual use of the aluminum alloys, their low hardness is extremely disadvantageous.

The object of the present invention is to obtain an aluminum material whose hardness is higher than any other commercial aluminum alloys by special treatments to 3,531,337 Patented Sept. 29, 1970 which the chemical ingredients of the aluminum alloy is subjected, and to make the aluminum material applicable as such screws, viz nuts, springs, and other parts of machines that require high abrasion resistance property as those of iron and steel.

The chemical ingredients contained in the present alloys are 2.67.8% zinc and 0.6-3.8% magnesium as the principal additive elements which mainly act as the components of age hardening. In addition to these, the present alloys contain 02-12% of each of iron and nickel of transition metals of Group IV of the Periodic Table, 0.1-1.2% manganese, and 0.5% chromium. At the same time, the alloys contain ODS-1.2% zirconium of Group IVa (in some cases, this being replaced in part with titanium 0r hafnium), 0.0050.3% boron which is a metalloid, and 0.050.85% silicon, and the remainder of aluminum.

The characteristics points in treating the alloys of the present invention are in that the molten metal is kept at elevated temperature after the melting of the alloys and in the nitrogenization of alloy which is carried out by passing nitrogen or a nitrogen-containing gas, for example, ammonium into the molten alloy to react with each other or by reacting a nitrogen-containing compound such as an ammonium-containing compound or a nitrate, so that zirconium of Group IV (in some cases, titanium or hafnium are included) is dispersion hardened as a zirconium nitride. Boron, also, forms in part boron nitride, and promotes the strengthening of dispersion.

Among other additive elements, iron, nickel and cobalt of Group IV of the Periodic Table form intermetallic compounds in the aging aluminum alloys. Further, in the case of single use of these hardening elements for the purpose of reducing the concentration thereof in the solid solution, 1% addition thereof is destructive, the simultaneous addition of at least two elements, however, hardly damaging the aging hardness.

Manganese has an effect to improve the fineness of grain size of crystal and toughness together with chromium, and since chromium increases the corrosion resistance, against especially stress corrosion, the addition of a small amount of chromium is effective. Also, the addition of a small amount of silicon which already exists in the raw metal contributes to the age hardening.

Thus, the present invention is an alloy melt prepared by adding the above-mentioned various elements to the aging aluminum-zinc-magnesium system, and subjecting the system to the nitriding treatment. The greatest characteristics of the present invention is to produce an alloy having hot and cold workabilities and at the same time such a high hardness produced by solution treatment and age hardening (T treatment) or the work hardening thereafter that has never been observed.

The examples of alloys of the present invention will he illustrated as Table 2.

TABLE 2.COMPOSITIONS IN EXAMPLES OF ALLOYS OF THE PRESENT INVENTION Zn Mg Ni Zr Fe Co B Si Mn Example 1 5. 0 2. 0 0. 4 0. 35 0. 4 0. 006 0. 4 0. 6 Example 9 5.0 2.0 0.2 0.35 0.8 0.6 0. l 0.18 0. 3

3 above-mentioned solution treatment, and artificial aging are as shown in Table 3.

TABLE 3.AGING I'IARDENING IN THE EXAMPLES OF ALLOYS OF THE PRESENT INVENTION Micro Vickers hardness Aging time (Chr.)

As shown in Table 3, the hardness reaches about 180 in the aging hardening conditions, which is the highest hardness in the conventional aluminum alloy. This hardness matches the hardness of hardened phosphorus bronze or that of medium carbon steel. Furthermore, when the aging hardening of the alloy of the present invention is stopped before the highest possible hardness is obtained by this treatment, it is possible to produce an amazingly high hardness of Vickers hardness 200 or more by applying about 50% cold work to this alloy. For example, the alloy of a Vickers hardness of 205 is obtained in Example 1, and a Vickers hardness of 201, in Example 2, these hardness being about twice of that imparted to duralumin 2017, and matching the hardness of copper alloy naturally or even that'of iron material.

The present alloy is, as explained above, an alloy having such a high hardness that ever seen as a wrought aluminum alloy having workability and as aluminum base alloy treated with T treatment. The present alloy also shows an extremely high hardness as casting material, and is further improved by solution and aging treatments (T treatment) after the alloy was cast.

The composition of the example and the aging hardness under such treatment condition as described above are as shown in Table 4.

TABLE 4.-CO1\IPOSITION AND AGING HARDNESS IN THE EXAMPLE OF CAST ALLOY OF THE PRESENT INVENTION Example 3 (Metal mold, cast): Zn, 5.0; Mg, 2.0; Ni,

0.55; Zr, 0.35; Fe, 0.7; Cr, 0.1; B, 0.1; Si, 0.35; Mn, 0.7.

Aging hardness (Micro-Vickers hardness: same as above) Cast condition: 127; Solution treatment: 84; Aging time (hr.): 18,157;40,169;45, 181.

The alloy of the present invention shows, as illustrated above, a considerable hardness (a Vickers hardness of 127) under casting condition. By the T treatment, the hardness of the present alloy reaches a Vickers hardness which is as high as 180, so that the aluminum alloy excellent in abrasion resistance is obtained as a casting product.

The aluminum alloy high in hardness to which the present invention relates demonstrates excellent properties produced by such a composition as was shown in the previous example, and by various treatments suited for the composition.

As to the behaviors of elements of the composition, zirconium (in some cases, titanium or hafnium being included) and boron become, as already explained above, dispersion particles by forming nitrides thereof by the solution treatment, and perform the action of dispersion strengthening by blocking the move of dislocation line. In this occasion, the suitable amount of zirconium or a metal of its group is 0.051.2%, and the amount of boron, 0.0050.3%. When the amount of any element is smaller that the lower limit, no effect is observed, while when the amount of the element exceeds the upper limit, the workability is damaged or the alloy perhaps becomes fragile.

Transition metal iron, nickel and cobalt of Group IV of the Periodic Table have very little solid solubility in aluminum, concentrate around crystalline grain boundary and strengthen the neibourfood of grain boundary by increasing the dislocation density, and promote the Work hardenings. The single use of these metals is in some cases, as described above, destructive to the age hardening, while the simultaneous use of at least two elements of these do not damage the age hardening, so that these elements are added simultaneously for these reasons. In this case, the suitable amount of each of these ingredients is in the range of 0.21.2%. When the amount is smaller than the lower limit, there is no practical effect, and when the amount exceeds the upper limit, the corrosion resistance is damaged, toughness, also, being reduced.

Chromium and manganese of the transition metals of Group IV check the deterioration of the grain boundary by making the crystalline grains finer similarly to the action of iron with an effect that corrosion resistance is increased. Both elements are very useful and especially when chromium is contained at 0.5% or below, the ingredient is effective particularly to casting alloys. 01-- 1.2% manganese has an effect of improving malleability. Silicon promotes the age hardening, and, similarly to the above-mentioned iron and other transition metals, has an effect of checking the deterioration of the grain boundary. The addition of a large amount of silicon, however, damages workability. Its suitable amount is in the range of ODS-0.88%.

What I claim is:

1. An aged aluminum alloy product high in hardness and abrasion resistance characterized by elevating the hardness of an alloy containing 2.6-7.8% zinc, 0.63.8% magnesium, 0.21.2% iron, 0.2-1.2% nickel and/or cobalt, 0.1-1.2% manganese, 0.5 or below of chromium, 0.05-1.2% of at least one element from the group consisting of zirconium, hafnium and titanium, said element being combined with nitrogen in the product to form dispersed nitrides; 0.0050.3% boron, at least a part of which is combined with nitrogen in the product to form dispersed nitrides, and 0.03-0.85% silicon, and the remainder of aluminum, said product having been made by subjecting said alloy to a nitriding treatment while in the molten state, and then to a solution heat treatment at a temperature in the range of 450490 C. as cast or after working and thereafter to an aging treatment at a temperature of to C. to produce a high hardness, and, in some cases, before the maximum hardness is obtained in the aging treatment, further subjecting the alloy to plastic working.

2. An alloy product of claim 1 comprising 5.0% Zn, 2.0% Mg, 0.4% Ni, 0.35% Zr, 0.4% Fe, 0.006% B, 04% Si and 0.6% Mn.

3. An alloy product of claim 1 comprising 5.0% Zn, 2.0% Mg, 0.2% Ni, 0.35% Zr, 0.8% Fe, 0.6% Co, 0.1% B, 0.18% Si and 0.3% Mn.

4. An alloy product of claim 1 comprising 5.0% Zn, 2.0% Mg, 0.55% Ni, 0.35% Zr, 0.7% Fe, 0.1% Cr, 0.1% B, 0.35% Si and 0.7% Mn.

References Cited UNITED STATES PATENTS 2,793,949 5/1957 Imich 75-138 X 3,171,760 3/1965 Vernam et al 75146 X 3,180,728 4/1965 Pryor et al. 75l38 3,262,762 7/1966 Bechtold 75l38 X 3,304,209 2/1967 Anderson et al. 75146 X 3,332,773 7/1967 Dudas 75146 3,468,658 9/1969 Herald et al. 75135 CHARLES N. LOVELL, Primary Examiner US. Cl. X.R.