EFFECT OF PRE-AGING ON MICROSTRUCTURE AND TENSILE PROPERTIES OF Al-Mg-Si ALLOYS

摘要

The demand for more lightweight, fuel efficient and enhanced performance automobiles lias stimulated research and development in high-strength and high formability aluminum alloys. Recent research has focused on the 6xxx series alloys[1-6], These alloys are medium to high strength, excellent formability and good corrosion resistance. The combination of these properties makes them potentially more desirable for certain applications than the stronger 7xxx alloys. The basic requirement for automotive sheet is to have a high formability so that the panels can be stamped while retaining, or preferably increasing in strength when the part is painted and thermally cured (baking)[7]. However, the holding time in the baking process is usually not long enough to lead to the peak aged condition for Al-Mg-Si alloys, so that the potential strength of Al-Mg-Si alloys can not be fully exerted. Hence, some methods must be used to: increase the strength of these alloys in the paint baked condition. Furthermore, in practical usage, it is usually difficult for artificial aging to be performed immediately after solution heat treatment, which means that a delay at room temperature prior to paint baking is usually unavoidable. Many studies[8-10] have been carried out on the effect of a delay at room temperature (natural aging) on the mechanical properties of Al-Mg-Si alloys. It is reported that the mechanical properties of Al-Mg-Si alloys obtained through artificial aging are influenced significantly by the natural aging. This problem has been extensively studied previously[11-14], and many methods are suggested to minimize the detrimental effect of natural aging. This paper reports on a pre-aging method which can improve the strength of two Al-Mg-Si alloys in a simulated paint baking condition.