The Role of Solutionizing Treatment on Microstructure, Mechanical and Corrosion Properties of AZ91 Magnesium Alloy

Abstract

In this research, AZ91 magnesium alloy was subjected to solutionizing at 410 °C for different soaking times (4, 8, 16, and 24 h), and the microstructure evolution, phase change, and mechanical and corrosion properties were investigated. From the microstructural studies, it was clearly observed that the intermetallic phase (Mg17Al12) appeared at the grain boundaries before heat treatment and was significantly altered after solutionizing. The X-ray diffraction studies after heat treatment clearly demonstrated a reduced fraction of intermetallic, which suggests the development of grains with super-saturated conditions due to the dissolved Al in the Mg lattice. Microhardness measurements showed decreased hardness (80.8 ± 2 HV0.1) with a lower level of variation within the measured values compared with the base alloy (93.6 ± 5.18 HV0.1). From the tensile test results, 8 h soaking time resulted in increased tensile strength up to 264.5 ± 6.1 MPa compared with the base alloy (171.6 ± 4.2 MPa) without sacrificing the % elongation. Further increasing the soaking time to 16 and 24 h did not improve the strength of the alloy. From the potentiodynamic polarization studies, lower corrosion current density values were observed for the samples with 8 and 16 h soaking time, which is attributed to the effect of lower intermetallic and homogeneous microstructure resulting from the heat treatment.