Effect of Rolling Shape Variation on Microstructure Characteristics and Degradation Performance for Mg-Zn-Sr-Zr-Mn Alloys

The influence mechanism of microstructure and film structure changes induced by the change of rolling shape variable on the degradation performance of hot-rolled magnesium alloy in physiological environment was studied by OM, XRD, SEM, static immersion and potentiodynamic electrochemical test. The results show that the degradation product layers of magnesium alloys with different rolling shape variables are mainly composed of Mg(OH)(2), MgCO3, CaHPO4 and HA. With the increase of rolling shape variable, the microstructure of Mg-Zn-Sr-Zr-Mn alloy becomes uniform gradually, and the degradation rate decreases from 1.03 mm.a(-1) to 0.24 mm.a(-1). This is because with the increase of rolling shape variable, the matrix grain is significantly refined, resulting in more grain boundaries, hindering the expansion of corrosion cracks, and acting as a barrier in the corrosion process of corrosive medium. In addition, with the increase of rolling shape variable, the second phase in the alloy is broken and dispersed, which reduces the density and intensity of galvanic corrosion in the alloy, promotes the uniform occurrence of corrosion and reduces the pitting pit. Finally, hot rolling can improve the defects of the corrosion film, provide more nucleation points for the oxide film on the surface of the alloy, and reduce the cracking of the oxide film. The compactness and stability of the oxide film are greatly improved with the increase of rolling shape variable, and further slow down the infiltration of corrosion ions.