New Al-Mg-Cu Alloys for Autobody Sheet Applications

Al-Mg-Cu alloys have been developed for auto body components. The improved characteristics are obtained by using a continuous annealing line (CAL) and applying final ageing. Rapid heating, high annealing temperature and rapid cooling of CAL dissolves Cu precipitates and recrystallizes in grains of suitable sizes to prevent stretcher strain marking free (SSP). The improved formability and increased strength after final ageing are due to the Cu dissolution by CAL. Other fabrication practices were also studied.

The paint bake properties are better than 5182-0 and the formability of these alloys do not change during long storage. Other properties such as weld-ability and corrosion resistance are almost comparable or superior.