| The application of aluminum alloy in automobile is of great significance to solve the environmental pollution and low energy shortage in China,while Al-Mg-Si alloy has become the main material for automobile aluminum alloy parts due to its moderate strength and good forming performance.Al-Mg-Si alloy is a heat treatable alloy,and its properties are related to the type,size and precipitation mechanism of the precipitate produced in the heat treatment process.It is important to understand the evolution of precipitated phase in the precipitation process to improve the properties of the alloy.In this paper,four heat treatment methods are designed to systematically study the precipitation behavior and mechanical properties of Al-Mg-Si alloy,so as to have a deep understanding of different heat treatment methods,fully tap the potential of materials and meet the needs of practical engineering applications.The main conclusions are as follows:（1）The Al-Mg-Si alloy heat treatment optimization,the optimum parameters of the solid solution and aging at 550℃-4 h,170℃-8 h.The precipitated phases were detected by SEM and EDS,and the alloy mainly consisted of spherical Mg2Si and stripα-Al Mn Fe Si phases.After solid solution quenching,there were five exothermic peaks in the DSC curve during the heating process at 10K/min,corresponding to the aging sequence of Al-Mg-Si alloy:SSSS→Mg-Si co-clusters→GP→β‘’→β’→β;（2）Along the direction of<001>Alobservation under the aging peak of Al-Mg-Si alloy,precipitated phase morphology is mainly spherical and needle.The precipitating mechanism of the alloy is as follows:in the early aging stage,the spherical Pre-β‘’is the main one,and as the aging process progresses.The spherical Pre-β‘’gradually dissociates to form the needleβ‘’phase,and at last,there are Pre-β‘’phase,β‘’phase andβ’phase in the peak aging time.（3）After solid solution and quenching,natural ageing and low temperature 60℃ageing can form groups cluster or GP zone,these atoms cluster is not stable and dissolved in subsequent aging process.It consumes the precipitation power of aging and reduces the precipitation rate and mechanical properties of the alloy.Aging at 90and 120℃high temperature can generate stable GP zone in the alloy,inhibit the formation of the natural aging clusters,and promote the precipitation of strengthening phase in the subsequent aging process,shortens the time of peak hardness and improve the hardness and tensile strength of the alloy.The morphology of tensile fracture shows ductile fracture,and a large number of micropores appear around the dimple mouth,and the size of the dimple mouth is uneven.（4）Pre-ageing at 170℃-30 min heat treatment is beneficial to the formation of GP area,and then 60℃-10 h interrupt aging lead to a large number of uniform distribution of spherical GPzone.The secondary aging showed the best comprehensive performance in the above heat treatment methods,which not only improved the hardness and tensile strength of the alloy,but also improved the elongation.In addition,the tensile fracture morphology presented an homaxial dimple,with an increased number of dimples and a smaller size and spacing of dimples. |
PDF Full Text Request