The corrosion mechanism of AZ31 magnesium alloy used as automobile components and the influence of the concentration of Cl- ion in simulated acid rain(SAR)were studied by electrochemical tests and SEM.The results show that pitting corrosion happens around the AlMn phases locating at the grain boundary.The corrosion of AZ31 magnesium alloy in SAR is controlled by the rate of anodic dissolution and hydrogen evolution,and the corrosion rate of AZ31 increases with increasing concentration of Cl- ion.However,the Cl- ion in SAR is not the main influencing factor inducing the pitting corrosion.