The Research Of Microstructure And Properties Of Al-Mg-Si-Cu Alloy With Germanium For Automobile Panels

Abstract:Because of excellent mechanical properties, corrosion resistance, formability, weldability and bake hardenability, Al-Mg-Si-Cu alloies are widely used in the Automobile panels for lightweight.Al-Mg-Si-Cu series automobile panels are usually produced by stamping forming at the T4state, then paint-baking at175℃. Due to the short time (generally less than30min) of the paint-baking, it is difficult to utilize the alloy’s potential of age hardening. Adding trace elememt, pre-tension, and preageing process are related to the precipitation of second phase. In this article, Ge element is added into the alloy., In order to find a reasonable heat treatment system and to give full tap the alloy’s potential of age hardening, research of the preageing and pre-draft process is conducted. The results are as follows:1) Unlike other atoms (Mg, Si, Cu, Mn), Ge has lower vacancy formation energy and strong vacancy binding energy, which not only effectively delay the natural aging phenomenon, but also accelerate the hardening rate of artificial aging. Because of more nucleation center in matrix, the precipitated particles are more dispersed, leading to an improvement of strength;2) After cold deformation, solute atoms usually gather around dislocations, because it is easy to meet the requirements of composition of the dislocation nucleation, which makes the second particles more dispersed. High density dislocations distributed in the alloy matrix provide more dispersion nucleation for the precipitation of second phase particles, which makes second phase particles smaller and more dispersed;3) Preageing makes the hardness of alloy to a relatively low value, which has less influence on the industrial properties, but has good influence on the bake hardening. Presaging can make the alloy have higher hardness values after bake aging, which is beneficial to the production of automobile panels;4) The scheme of175℃/20min preageing+3%pre-stretching (T4P) not only can effectively prevent the negative impact of natural aging on bake aging, but also accelerate the bake hardening rate. This kind of aging and stretching makes the alloy meet the requirements of automobile body sheet after175℃/30min bake aging.