Effect of Processing and Environment on Mechanical Properties of Die Cast Magnesium Alloys

Effect of die casting variables and corrosive media on impact, fatigue and creep behavior of Mg alloys was investigated. A new synergistic effect of corrosion and stress on the viscoelasticity of magnesium alloys has been shown. This phenomenon, named corrosion creep, has been studied in die cast AZ91D (Al, 9%; Zn, 1%; Mg - the rest), AM50 (Al, 5%; Mn, 0.4%; Mg-the rest) and AS21 (Al, 2.3%; Si, 1.1%; Mg - the rest) alloys. Electrolytes of the following compositions were used: borate buffer solution (pH = 9.3) for corrosion creep tests, 3.5% NaCl or borate buffer solution for corrosion fatigue tests. σ-N curves for AZ91D and AM50 alloys were obtained to predict the lifetime of these alloys in corrosive media. The surface layer of die cast alloys influences their impact and plastic behavior in a crucial manner. Its removal from one side of a standard specimen (10 x 10 x 50mm) by a mechanical treatment leads to a (1.9-2.8)-fold decrease in the impact strength of AZ91D and AM50 alloys.