Table 1. Composition of the Experimental Alloys. Alloy
Chemical Analysis, wt. % Number
10 11
12 13
15 2 Cu Mg Si
2.2 2.2
- 0.43 -
0.78 0.47 - Ni Mn Other
0.47 0.46
2 0.84 0.80 0.47 2 0.98
1.9 0.92 0.52
0.48 Sc, Ti 0.47
Sc, Ti 0.46 Sc, Ti 0.55 0.23 Sc, Ti 0.48 Sc, Ti
Procedure An induction furnace was used to prepare
fi ve experimental alloys. Either A206 ingot or pure aluminum was the starting material for preparing the alloys. Alloying additions were
made as master alloys or pure metals. In each experiment, 44 lbs. (20 kg) of the alloy was prepared. T e composition of the alloy was tested using optical emission spectrograph be- fore casting. Most of the melts were designed as split melts with extra alloy additions and carried out after the fi rst set of experiments. T e fi nal composition was evaluated by wet chemical analysis. Permanent mold cast plates (6 x 4 x 0.5 in. [150 x 100 x 12.5 mm]) or rods (0.7- in. [19-mm] diameter) were produced to obtain test coupons. The test coupons were subjected
The solution treatment temperature varied from 977F to 1,094F (525C to 590C). The coupons were aged at 572F (300C) for several different durations. Hardness was measured on the test coupons to assess strength for each alloy chemistry and heat treat- ment. After optimization, some of the selected alloys were soaked at 482F (250C) for up to 1,000 hours. Their
to thermal treatments designed to facilitate the precipitation of Al3
Sc.
Fig. 1. Shown are the hardness results for alloys 10, 11 and 12 after solution treating at 977F (525C) and aging at 572F (300C).
response was measured using hardness testing. After heat treatment, the alloys were subjected to long-term expo- sure testing at 482F (250C). To establish casting process parameters and evaluate the
castability of one of the alloys, a 1,000-lb. lot was com- mercially prepared and tested. In preparation for determin- ing tensile and fatigue properties of the alloy at elevated temperatures, a study was performed to establish the heat treatment parameters that would maximize the properties at 482F (250C).
Fig. 2. This air-cooled cylinder head was used to assess the castability of alloy 13
May/Jun 2012 | METAL CASTING DESIGN & PURCHASING | 43
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