Effect of tool rotational speed on the microstructures and tensile properties of 7075 aluminum alloy via Friction Stir Process (FSP)

7075-T6 aluminum alloy plates were subject to FSP with various tool rotational speeds (1230, 1450 and 1670 rpm) followed by different heat treatments (natural aging and T4T6 treatments). The influences of tool rotational speeds and aging treatments on the microstructures and tensile properties were discussed. The experimental results showed that the tensile strength of FSPed specimens with various tool rotational speeds were close. After aging treatments, higher tool rotational speeds (1670 rpm) had an embrittlement phenomenon on the SZ due to the contribution of low element bands (LEBs) and precipitates. EPMA analysis showed that the LEBs are low element distributions, such as Zn, Mg, Cu. Decreasing the tool rotational speeds, the LEBs were not obvious and restrained the brittle behavior to improve the ductility. Compared with natural aging, after T4T6 treatments, the tensile strength of FSP specimens with all tool rotational speeds was improved obviously.