952 New Aluminum Automotive Alloys

The need to reduce emissions while enhancing performance and adding features has driven manufacturers to use more aluminum in automobiles and light trucks. This effort has been accompanied by the development of new aluminum alloys specifically tailored for these applications. These alloys are too new to be listed in ASTM specifications or Aluminum Standards and Data, so detailed information is given here.

Since automobiles and light trucks undergo a paint bake cycle at temperatures high enough to affect the temper of both heat-treatable and non-heat-treatable aluminum alloys, the automotive alloys are provided in the -T4 (solution heat treated) and -O (annealed) tempers, respectively. Both have the best formability in these tempers for the cold working they undergo in the process of being formed into body panels. The forming operation increases strengths through cold working. The subsequent paint bake artificially ages the heat-treatable alloys, which can additionally increase their strength, but reanneals the non-heat-treatable alloys, erasing any strength increase due to cold work. High strength is not necessarily important in this application, however.

The automotive alloys fall in three groups:

• 2xxx series (aluminum-copper alloys), including 2008, 2010, and 2036. Alloys 2008 and 2010 were developed to provide improved formability over 2036. Alloy 2036 has more copper than 2008 and 2010, giving it about 40% higher strength but less corrosion resistance. These alloys are heat treatable.

• 5xxx series (aluminum-magnesium alloys), including 5182 and 5754. Alloy 5182 was developed for the ends of beverage cans. It has high magnesium content, providing high strength but also sensitivity to corrosion if exposed to temperatures above 150°F for extended periods. Alloy 5754 is a variant on 5454, with slightly more magnesium (3.1 vs. 2.7%), lower strength, but better formability.

• 6xxx series (aluminum-magnesium-silicon alloys), including 6009, 6111, and 6022. These alloys are heat treatable and can attain fairly high strengths during the paint bake cycle. The newest of these alloys, 6022, is used in the Plymouth Prowler body panels.

Extrusions have not seen significant automotive use, but some alloys such as 7029 have been used in bumpers for some time.

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