Effects of aging treatment and pre-deformation on stress corrosion cracking of magnesium alloy

Abstract

As a medical implant material, the mechanical degradation behavior of magnesium alloy in service environment is of great significance. The Mg–4Zn–0.1Sr alloy is an ideal biomedical alloy, while solute Zn atoms are easy to cause the stress corrosion cracking (SCC) of the alloy. In this paper, the distribution of Zn atoms in Mg–4Zn–0.1Sr alloy is changed by aging treatment, so as to reduce the SCC of the alloy promoted by the Portevin-Le Chatelier effect. In comparison with the as-solutionized alloy, the tensile strength and the elongation of the alloy aged at 160 °C for 400 h in Hanks' solution are increased by 42% and 107%, respectively. In order to improve the aging kinetics, twins and dislocations are introduced by pre-compression. Twins and dislocations promote the diffusion of Zn atoms during aging treatment and make the distribution of precipitates more dispersed. The dislocations can be recovered by aging treatment to avoid promoting anodic dissolution and hydrogen embrittlement. Twin boundaries cannot easily migrate due to the nailing of Zn atoms, the latter of which improves the mechanical properties and leads to grain refinement, and have a good effect on reducing the anodic dissolution rate of the alloy. In comparison with the as-solutionized alloy, the tensile strength and the elongation of the alloy with 3% pre-compression and aging at 160 °C for 200 h are increased by 47% and 77%, respectively. The mechanism of mechanical property improvement of the alloy in Hanks' solution by the thermomechanical treatment is revealed.

Keywords

• Magnesium alloy
• Heat treatment
• Pre-deformation
• Microstructure
• Stress corrosion