Patent ID: 12194529

DETAILED DESCRIPTION

Example 1—Plate Testing

Various Al—Li alloys were cast as ingot and homogenized. The composition of each ingot is shown in Table 3a, below. Alloys A and B are invention alloys. Alloy C and the 2070 alloy are non-invention alloys. The 2070 alloy is described in, for instance, commonly-owned U.S. Patent Application Publication No. 2012/0225271.

TABLE 3aCOMPOSITION OF ALLOYSAlloySiFeCuMnMgZnLiZrTiA-10.020.033.570.290.240.940.920.100.02A-20.050.033.460.320.271.000.940.100.02B0.040.042.960.320.211.420.980.090.02C0.050.043.700.330.380.840.970.100.0220700.020.033.480.300.220.361.130.100.02

The balance of each alloy was aluminum, incidental elements and impurities, with no one impurity exceeding 0.05 wt. %, and with the total amount of impurities not exceeding 0.15 wt. %. After homogenization, the alloys were hot rolled to final gauge, solution heat treated, quenched and stretched about 6%. Approximate final gauges are provided in Table 3b, below.

TABLE 3bALLOYS AND FINAL GAUGEFinal GaugeFinal GaugeAlloy(mm)(in.)A-1(i)1003.94A-1(ii)1505.91A-2(i)1003.94A-2(ii)1505.91B(i)1003.94B(ii)1505.91C(i)1003.94C(ii)1505.912070(i)1003.942070(ii)1204.72

Various two-step artificial aging practices are completed on the alloys, the first step being completed at 290° F. (143.3° C.) for various times, as provided in Table 4, below, the second step being 12 hours at 225° F. (107.2° C.). Various mechanical properties of the aged aluminum alloy plates are measured in accordance with ASTM E8 and B557. Fracture toughness properties of some samples were also measured and in accordance with ASTM E399. As shown by the below data and correspondingFIG.1-2, the invention alloys realized an improved combination of properties in the short transverse direction.

TABLE 4Mechanical Properties (Short Transverse Direction)1stStepAge TimeTYS(ST)UTS(ST)Elong.KIC(S-L)Alloy(hrs)(MPa)(MPa)(ST)(%)(MPa-sqrt-m)A-1(i)25461.3526.03.221.6A-1(i)30466.1531.93.723.1A-1(i)50482.6543.33.120.9A-2(i)25466.0529.04.721.2A-2(i)30484.0543.03.819.1B(i)40446.1509.53.725.9B(i)60451.3511.64.124.7C(i)25473.3538.52.819.7C(i)45497.5555.02.119.22070(i)30467.8535.03.320.52070(i)50489.5548.82.415.8A-1(ii)30460.2515.73.120.5A-1(ii)50475.4521.22.020.4A-2(ii)25442.0496.03.624.7A-2(ii)25443.8495.03.022.5A-2(ii)30451.5504.03.022.9B(ii)40440.2484.02.822.1B(ii)60443.0489.52.523.5C(ii)25465.1517.52.719.0C(ii)45486.1534.02.218.72070(ii)30461.3527.43.418.2*(120 mm)2070(ii)50482.6538.12.716.5*(120 mm)*= KQvalue

At 100 mm, the new alloys generally realize improved fracture toughness at equivalent strength. For instance, invention alloy A-1 realizes about 3 MPa-sqrt-m higher strength over the 2070 alloy at about equivalent strength (at 30 hours of aging). Invention alloy A-2 also is improved over the 2070 alloy, and the A-2 alloy would be expected to achieve results similar to that of the Alloy A-1 if the silicon content of the A-2 alloy were reduced to 0.02 wt. %. Invention alloy B realizes very high fracture toughness at reduced strength levels, but would be expected to achieve results at least as good as A-1, if aged to equivalent strength. The improved properties are even more pronounced at 150 mm, where all of the invention alloys realized much better fracture toughness at equivalent strength. Notably, the invention alloys include less magnesium than non-invention alloy C. The invention alloys also have a Cu:Zn ratio (weight) of not greater than 4.25:1, whereas the non-invention alloys realize higher Cu:Zn ratios. The invention alloys also have more zinc than alloy C and non-invention alloy 2070.

The stress corrosion cracking (SCC) resistance properties of many of the alloys were tested in the ST direction and in accordance with ASTM G44/G47. All of the invention alloys at all aging conditions realized, or were expected to realize, no failures at net stresses of 310 MPa and 379 MPa over a period of 30 days of testing (some alloys are still in test). Conversely, alloy C realized multiple failures at net stresses of 310 MPa and 379 MPa within the 30 day period and under the same testing conditions. This may be due to the fact that alloy C includes high magnesium, which may make alloy C prone to stress corrosion cracking. Alloy C could be aged further to improve corrosion, but its already poor fracture toughness would decrease. Conversely, invention alloys A and B achieve a good combination of four properties: strength, elongation, fracture toughness and stress corrosion cracking resistance.

Example 2—Additional Plate Testing

Three additional Al—Li alloys (all invention) were cast as ingot and homogenized, the compositions of which are shown in Table 5, below.

TABLE 5Compositions of Example 2 AlloysAlloySiFeCuMnMgZnAgLiZrTi10.040.043.460.270.260.98—0.960.100.0320.070.073.630.270.260.97—0.960.090.0230.060.043.500.260.220.96—0.970.090.02
The balance of each alloy was aluminum, incidental elements and impurities, with no one impurity exceeding 0.05 wt. %, and with the total amount of impurities not exceeding 0.15 wt. %. After homogenization, the alloys were hot rolled to final gauge, solution heat treated, quenched and then stretched about 6%. The alloys were then artificially aged at various times and temperatures. The aging conditions are shown in Table 6.

TABLE 6Aging Conditions for Example 2 AlloysConditionFirst StepSecond StepA20 hours at 290° F.12 hours at 225° F.B30 hours at 290° F.C40 hours at 290° F.
The alloys were cooled to room temperature between aging steps.

The through-thickness mechanical properties of the alloys were then tested, the results of which are shown in Table 7, below.

TABLE 8SCC test results (days in test)Final GaugeAgingSampleSampleSampleAlloy(mm)Condition123159.8ATTTBTTT260.8ATTTBTTT3107.4ATTTBTTTT = still had not failed after 20 days in test.

As shown inFIG.3, Alloys 1-2, having a thickness of about 60 mm, realize an excellent combination of strength and fracture toughness. Alloy 3 realizes a similar strength-toughness trend as the 100 mm alloys of Example 1.

The stress corrosion cracking (SCC) resistance properties of many of the alloys were also tested in the ST direction as per Example 1 at a net stress of 310 MPa. The results are provided in Table 8, below.

TABLE 7Mechanical Properties of Example 2 AlloysFinalSTSTSTS-LGaugeAgingTYSUTSElong.KICAlloy(mm)Condition(MPa)(MPa)(%)(MPa√m)159.8A4555357.827.3B4645427.323.9C4735488.522.7260.8A4545237.822.7B4645327.021.8C4685385.321.33107.4A4435106.022.7B4605245.822.0C4635235.022.3

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.