Effect of Step Quenching on Mechanical and Corrosion Properties of Al-Mg-Si-Cu Alloy
Effect of step quenching at different temperatures on mechanical and corrosion properties of Al-Mg-Si-Cu alloy was explored by carrying out room temperature tensile test,intergranular corrosion test,electrochemical corrosion test,as well as by means of transmission electron microscopy(TEM).It is found that the alloy,after 60 minutes of step quenching at 100℃followed by 28 days of natural aging,can not only maintain a low yield strength of 162.49 MPa and a high strengthening increment of 105.60 MPa,but also exhibit a 57.2％reduction in intergranular corrosion depth compared to water-quenched alloy.TEM and EDS analyses show that type Ⅱ Mg-Si clusters formed during step quenching effectively inhibit type Ⅰ clusters formed during natural aging,while promote precipitation of intergranular β″ phase and β′ phase.Moreover,the precipitated phase at grain boundary is coarse and spherical with discrete distribution due to depletion of nearby solute atoms.
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