Corrosion Stress Relaxation in Magnesium Alloys

Abstract

The principal drawback of magnesium as a structural material, besides its relatively low corrosion resistance, is poor stress relaxation characteristics [1], which limit Mg alloys application in automotive and aerospace industry. It is well known [2, 3] that the relaxation behavior of a material is characterized by a spectrum of relaxation times or a relaxation spectrum H(). To the first approximation, H()= [dE(t)/dlnt]t= where  is the relaxation time, E(t) = t is the relaxation modulus; t is the current time, tisthe current relaxation stress changing from the initial value of stress  (t=0) to its final value (the remaining stress) rem, is the initial (usually elastic) strain corresponding to the stress . The relaxation time corresponding to the maximum of the function H(), as well as the remaining stress, is accepted as characteristics of stress relaxation [2, 3]. Earlier we have found that the relaxation time strongly depends on casting parameters and porosity. It varied in AZ91D alloy at 150 o C from 10 to 20 hours [4]. The present paper deals with the corrosion stress relaxation behavior of pure Mg and die-cast Mg alloys in 3.5% NaCl (pH ≈ 5) and 0.1N Na2B4O7 solution with a stable pH 9.3.