7XX aluminum casting alloys, and methods for making the same

Abstract

New shape-cast 7xx aluminum alloys products are disclosed. The new shape-cast products may include from 3.0 to 8.0 wt. % Zn, from 1.0 to 3.0 wt. % Mg, where the wt. % Zn exceeds the wt. % Mg, from 0.35 to 1.0 wt. % Cu, where the wt. % Mg exceeds the wt. % Cu, from 0.05 to 0.30 wt. % V, from 0.01 to 1.0 wt. % of at least one secondary element (Mn, Cr, Zr, Ti, B, and combinations thereof), up to 0.50 wt. % Fe, and up to 0.25 wt. % Si, the balance being aluminum and other elements, wherein the aluminum casting alloy include not greater than 0.05 wt. % each of the other elements, and wherein the aluminum casting alloy includes not greater than 0.15 wt. % in total of the other elements.

Claims

1. A method comprising: (a) shape casting a 7xx aluminum casting alloy into a shape-cast part, wherein the 7xx casting alloy consists of: (i) from 3.0 to 8.0 wt. % Zn; (ii) from 1.0 to 3.0 wt. % Mg; wherein the wt. % Zn exceeds the wt. % Mg; (iii) from 0.35 to 1.0 wt. % Cu; wherein the wt. % Mg exceeds the wt. % Cu; (iv) from 0.05 to 0.30 wt. % V; (v) from 0.01 to 1.0 wt. % of at least one secondary element, wherein the at least one secondary element is selected from the group consisting of Mn, Cr, Zr, Ti, B, and combinations thereof; wherein, when present, the aluminum casting alloy includes not greater than 0.50 wt. % Mn as a secondary element; wherein, when present, the aluminum casting alloy includes not greater than 0.40 wt. % Cr as a secondary element; wherein, when present, the aluminum casting alloy includes not greater than 0.25 wt. % Zr as a secondary element; wherein, when present, the aluminum casting alloy includes not greater than 0.25 wt. % Ti as a secondary element; wherein, when present, the aluminum casting alloy includes not greater than 0.05 wt. % B as a secondary element; (vi) up to 0.50 wt. % Fe (vii) up to 0.25 wt. % Si; and (viii) the balance being aluminum and other elements, wherein the aluminum casting alloy includes not greater than 0.05 wt. % each of the other elements, and wherein the aluminum casting alloy includes not greater than 0.15 wt. % in total of the other elements; wherein the shape casting process is selected from the group consisting of low pressure die casting, gravity permanent mold casting, semi-permanent mold casting, sand mold casting and centrifugal casting; (b) solution heat treating and then quenching the shape-cast part; and (c) artificially aging the shape-cast part to a T6 or T7 temper: wherein the shape-cast part is stress corrosion cracking (SCC) resistant being capable of passing SCC testing in accordance with ASTM G109-97(2011), wherein the SCC testing is conducted at a net stress of 240 MPa for 14 days, wherein 5 specimens are tested, and wherein all 5 specimens do not fail during the 14 days of testing.

2. The method of claim 1, wherein the shape casting process is low pressure die casting.

3. The method of claim 1, wherein the 7xx casting alloy includes not greater than 0.20 wt. % V.

4. The method of claim 1, wherein the 7xx casting alloy includes not greater than 0.18 wt. % V.

5. The method of claim 1, wherein the 7xx casting alloy includes not greater than 0.16 wt. % V.

6. The method of claim 1, wherein the 7xx casting alloy includes not greater than 0.14 wt. % V.

7. The method of claim 1, wherein the 7xx casting alloy includes at least 0.07 wt. % V.

8. The method of claim 1, wherein the 7xx casting alloy includes at least 0.09 wt. % V.

9. The method of claim 1, wherein the shape-cast part is an automobile part.

10. The method of claim 9, wherein the automotive part is a body-in-white (BIW) part or a suspension part.

Description

DETAILED DESCRIPTION

Example 1

(1) Several 7xx aluminum casting alloys having the compositions shown in Table 1, below, were cast via directional solidification. The dimensions of the directionally solidified alloys were approximately 25.4 mm (1 inch) thick, 102 mm (4 inches) wide, and 254 mm (10 inches) long.

(2) TABLE-US-00001 TABLE 1 Composition of Example 1 Alloys (in wt. %) Actual Composition, wt. % Alloy Zn Mg Cu Fe Si Mn Ti V Zr B A1 4.21 1.55 0.65 0.08 0.05 0.05 0.07 0.009 0.09 0.02 A2 4.20 1.56 0.65 0.08 0.05 0.05 0.07 0.057 0.09 0.02 A3 4.35 1.62 0.63 0.08 0.05 0.05 0.06 0.103 0.09 0.02 A4 4.33 1.63 0.63 0.08 0.05 0.05 0.07 0.151 0.09 0.02 Alloys A2-A4 are invention alloys.

(3) After casting, the alloys were solution heated by heating from room temperature to about 515.6° C. (960° F.), in about 2 hours, holding at about 515.6° C. (960° F.) for 6 hours, and then quenching in boiling water. The alloys were then naturally aged for about 12-24 hours, and then artificially aged by heating to about 204° C. (400° F.) in about 50 minutes, holding at about 204° C. (400° F.) for about 10 minutes, cooling to 182° C. (360° F.) in about 15 minutes, holding at 182° C. (360° F.) for about 4 hours, and then air cooling to room temperature.

(4) The Stress corrosion cracking (SCC) resistance of the alloys was then in accordance with ASTM G103-97(2011), the “Standard Practice for Evaluating Stress-Corrosion Cracking Resistance of Low Copper 7XXX Series Al-Zn-Mg-Cu Alloys in Boiling 6% Sodium Chloride Solution”. A stress level of 240 MPa was used for all specimens evaluated. Five replicated SCC specimens were used for each alloy. The SCC results are shown in Table 2, below.

(5) TABLE-US-00002 TABLE 2 SCC boiling salt test results of Example 1 Alloys Alloy Days to Failure A1 10 OK 14 2.91 OK 14 5.9 A2 7.23 OK 14 OK 14 12.02 OK 14 A3 OK 14 OK 14 OK 14 OK 14 OK 14 A4 OK 14 OK 14 OK 14 OK 14 OK 14 “OK 14” = passed 14 days of testing without failure.

(6) The addition of vanadium improves the SCC performance of the Al-Zn-Mg-Cu alloys. Two specimens of alloy Al failed within one week in boiling salt tests, whereas the specimens of vanadium-containing alloys passed 1-week boiling salt tests without failure. Larger vanadium content leads to improved SCC performance. Two SCC specimens of alloy A2 (0.057 wt. % V) failed in between one to two weeks, while specimens of A3 (0.103 wt. % V) and A4 (0.151 wt. % V) passed two weeks without any failures.

(7) The mechanical properties of the alloys were also tested in accordance with ASMT B557 and E8, the results of which are shown in Table 3, below. Adding vanadium did not materially impact tensile or yield strength, but did decrease elongation slightly.

(8) TABLE-US-00003 TABLE 3 Mechanical Properties of Example 1 Alloys Yield Strength, Tensile Strength, Elongation, Alloy MPa MPa % A1 320.8 376.0 11.0 A2 305.9 365.4 10.3 A3 323.4 376.9 9.0 A4 321.3 375.0 9.0

Example 2

(9) Several 7xx aluminum casting alloys having the compositions shown in Table 4, below, were prepared as per Example 1. SCC and mechanical properties were again measured using the same ASTM tests and conditions used in Example 1, the results of which are shown in Tables 5-6, below.

(10) TABLE-US-00004 TABLE 4 Composition of Example 2 Alloys (in wt. %) Actual composition, wt. % Alloy Zn Mg Cu Fe Si Mn Ti V Zr B B1 4.39 1.61 — 0.10 0.05 0.05 0.07 0.11 0.093 0.02 B2 4.38 1.61 0.25 0.10 0.05 0.05 0.07 0.11 0.093 0.02 B3 4.38 1.62 0.48 0.10 0.05 0.05 0.07 0.10 0.091 0.02 B4 4.39 1.61 0.78 0.10 0.05 0.05 0.07 0.11 0.091 0.02 Alloys B3 and B4 are invention alloys.

(11) TABLE-US-00005 TABLE 5 SCC boiling salt test results for Example 2 Alloys Alloy Days to Failure B1 0.08 0.08 0.08 0.08 0.08 B2 0.08 0.75 3.74 0.75 0.92 B3 OK7 OK7 OK7 OK7 OK7 B4 OK7 OK7 OK7 5.77 OK7 “OK 7” = passed 7 days of testing without failure.

(12) TABLE-US-00006 TABLE 6 Mechanical Properties of Example 2 Alloys Yield Strength, Tensile Strength, Alloy MPA MPA Elongation, % B1 268.5 323.0 12.0 B2 284.5 338.8 10.3 B3 301.5 353.8 8.7 B4 323.0 367.2 6.7

(13) As shown in Table 5, copper had a significant impact on SCC performance. All specimens of the alloy without copper (B1) failed in less than 2 hours (0.08 days). All specimens of the alloy with 0.48 wt. % Cu (B3) passed 7 days of testing at a stress level of 240 MPa. As shown in Table 6, increasing copper generally increases strength, but decreases elongation.

(14) While various embodiments of the present disclosure have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present disclosure.