. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CASTING INNOVATIONS
New Aluminum Alloy Handles the Heat A
luminum casting alloys have maximum effective operating temperatures of about 392F (200C), which is equal to their aging
temperatures. Historically, few, if any, aluminum alloys have been used above 392F. While this is adequate for most traditional applications, some indus- trial and military applications demand lightweight alloys used in the 482-572F (250-300C) range. An aluminum-copper-scandium
alloy that possesses good strength at temperatures as high as 482F has been developed with similar cast- ing characteristics to alloy A242. In a recent study performed by Eck Industries, Manitowoc, Wis., fi ve Al- Cu-Sc alloys were tested for hardness to determine their performance at el- evated temperatures (Table 1). Opti- mal heat treatment methods were es- tablished for the alloys. Three alloys were solution treated at 977F (525C) and aged at 572F. The two other al- loys (with magnesium content) were solution treated at 560F (293C) and 590F (310C) and then aged at 572F. After heat treatment, each alloy was subjected to a long-term exposure test at 482F. Samples were exposed for 1,000 hours. The results indicated an Al-Cu-Sc alloy (referred to as 13) with solution treatment at 590F re- tained its hardness, while the other
The metalcaster successfully produced this air-cooled cylinder head in an experimental Al-Cu-Sc alloy.
alloys exhibited softening to varying degrees (Table 2). A 1,000-lb. lot of the experimental
alloy was commercially prepared and used to establish casting process pa- rameters and evaluate its castability. Eck Industries chose to cast an air-
Table 1. Composition of the Experimental Alloys Chemical Analysis (weight %) Mg - -
Alloy 10 11 12 13 15
13a 15
15a
As-Cast 62 59 81 83 83 79 79
Cu 2.2 2.2 2 2
1.9 Si
0.84 0.98 0.92
Solution-Treated 48 53 68 77 56 79 79
0.43 0.78 0.8
0.47 -
Ni
0.47 0.46 0.47 0.55 0.52
cooled cylinder head in the experi- mental Al-Cu-Sc alloy with section sizes varying from 0.12 to 0.59 in. (3 to 15 mm). Traditionally, the cylinder head is cast in A242, an alloy with good high temperature strength and moderate castability. The metalcasting facility found the experimental alloy produced castings similar to those made in A242. Ultimately, the developed Al-Cu-
Mn
0.48 0.47 0.46 0.23 0.48
Table 2. Effect of 1,000 Hours of Exposure at 482F on Brinell Hardness Alloy 10 11 12 13
Other Sc, Ti Sc, Ti Sc, Ti Sc, Ti Sc, Ti
Aged 6 Hours Exposed 1,000 Hours 63 60 69 77 84 80 80
62 57 60 71 80 75 75
48 METAL CASTING DESIGN & PURCHASING
Sc alloy will be used to produce a metal matrix composite. The addition of micron-sized non-reactive ceramic particles to the developed alloy will show further increases in elevated temperature tensile properties. One potential application for the alloy is aluminum impellers in medium and heavy-duty diesel engines where air temperatures can reach 500F (260C) or higher. The temperature limit for the currently used 354-T61 aluminum cast impellers is 347F (175C).
METAL
This article was based on a paper presented at the 115th
Metalcasting Congress. Visit
www.moderncasting.com to read the full text. MAY/JUNE 2011
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