PRODUCT INNOVATIONS
Al-Cu-Sc Alloy Developed for High Temps Aluminum casting
alloys have maximum ef- fective operating tem- peratures 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 applica- tions, some industrial and military applications demand lightweight al- loys capable of being used in the 482-572F (250- 300C) range. One approach to enhancing the high temperature performance of aluminum alloys is in-situ formation of fine and thermally stable intermetallic phases in the metal matrix that will not coarsen at elevated temperatures. An aluminum-copper-scandium alloy possessing good strength at temperatures as high as 482F has been developed with this precipita- tion hardening method. In a recent study performed by Eck Industries, Manitowoc, Wis., five Al-Cu-Sc alloys were tested for hardness to determine their performance at elevated temperatures. Optimal heat treatment methods were established for the alloys. Tree alloys were solution treated at 977F (525C) and aged at 572F. Te two other alloys (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. Te results indicated an Al-Cu-Sc alloy with solution treatment at 590F retained its hard- ness, while the other alloys exhibited softening to varying degrees. A 1,000-lb. lot of the experimen-
tal alloy was commercially prepared and used to establish casting process parameters and evaluate its castability. Eck Industries chose to cast an air- cooled cylinder head in the experi-
produced castings similar to those made in A242. Further experimentation
Shown is the microstructure of the experimental alloy after heat treatment that consisted of solutioning at various temperatures for four hours, quenching at 192F (89C) and aging at 572F (300C).
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. Te metalcasting facility found the experimental alloy
for the Al-Cu-Sc alloy will focus on developing the alloy and determining ther- mal and casting processing parameters. Ultimately, the developed Al-Cu-Sc alloy will be used to produce a metal matrix composite. Te addition of micron- sized non-reactive ceramic particles to the developed alloy will show further increases in elevated tem- perature 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. Te temperature limit for the currently used 354-T61 aluminum cast impellers is 347F (175C).
This article is based on a paper presented at the 115th Metalcasting Congress. Visit
www.moderncasting. com to read the full text.
This air-cooled cylinder head was successfully cast in the experimental Al-Cu-Sc alloy. July 2011 MODERN CASTING | 45
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