Synergy of Sn micro-alloying and thermomechanical processing on formability and precipitation behavior of Al-Mg-Si-Cu-Zn alloys

The effect of Sn micro-alloying on microstructure evolution, formability and precipitation behaviour of Al-Mg-Si-Cu-Zn alloys were systematically studied by experimental techniques and theoretical calculations. Results show that Sn addition can accelerate both the precipitation and re-dissolution of the Fe-rich phase during casting and homogenising treatments, which thereby determined the final microstructure. A significant retarding effect to natural ageing precipitation was observed with increasing Sn content in quenching samples, but this effect was weakened in pre-aged samples, as explained by DSC and simulations. The different number densities of the strengthening phase beta '' at the same artificial aging state are mainly attributed to the changed activation energy of the beta '' phase affected by the formed Sn-containing Mg-Zn clusters and Mg-Si clusters. Trace Sn participating in the formation of GP zones, Sn-containing MgZn2 phase and new precipitating sequences during ageing were proposed for the first time.