Effect of Extrusion Temperature on the Mechanical Properties and Corrosion Behavior of LZ91 Alloys

Microstructural observations,tensile tests,potentiodynamic polarization measurements,and corrosion morphology examinations are conducted to investigate the effect of extrusion temperature on the mechanical properties and corrosion behavior of LZ91 alloys.The results show that the tensile strength of the LZ91 alloy is increased by 86 MPa after extrusion at 25℃.Meanwhile,the corrosion resistance is improved by about 2.7 times,and the maximum corrosion depth is decreased by 60μm.The increase in the tensile strength can be mainly attributed to theα-Mg precipitate strengthening inβ-Li.The improvement of the corrosion resistance is due to the fact that the nano-sized MgLiZn and refinedα-Mg precipitates inβ-Li weaken the effect of the cathodic phase on micro-galvanic corrosion,thereby decreasing the cathodic current density and local corrosion susceptibility.However,when the extrusion temperature is increased to 300°C,the corrosion rate is significantly accelerated due to the increase of the micro-galvanic corrosion caused byα-Mg precipitate coarsening at high temperatures.