TWO-STEP AGING BEHAVIOR IN AL-MG-SI ALLOYS FOR BODY PANEL OF AUTOMOBILE

摘要

The age hardenable Al-Mg-Si alloys become very attractive due to their good age-hardening response during a paint bake process at 170°C for 1.2 ks, i.e., bake-hardening (BH). There are two types of nanoclusters in Al-Mg-Si alloys. Cluster (1) and Cluster (2) formed at around room temperature and 100°C in Al-Mg-Si alloys, respectively. Due to the limited production process, the negative effects of two-step aging on the mechanical properties are caused in the age hardenable Al-Mg-Si alloys. The hardness is increased during natural aging (NA) due to the formation of Cluster (1) in the 3M4S and 3M10S alloys. The hardness is more increased in the 3M10 than that of the 3M4S. It is noted that the formation of Cluster (1) is accelerated by the addition of Si. The hardness does not increase at the early stage of two-step aging during aging at 170°C. The negative effect of two-step aging is confirmed. Meanwhile, the hardness is decreased at the early stage of aging at 170°C when the NA is performed for 2 month. It means that Cluster (1) is thermally unstable during aging at 170°C. The multi-step aging is designed to understand the role of Cluster (2) in the age-hardening behavior. The hardness is increased after pre-aging (PA). The hardness increase is suppressed during NA after PA, and the hardness is increased during aging at 170°C for 1.2 ks.