The elastic modulus of cast Mg–Al–Zn alloys

The effect of grain size, temper and solute content on elastic modulus values of pure Mg, a Mg–0.3Zr alloy, an AZ91 alloy and a number of Mg–Al and Mg–Zn binary alloys have been determined using two ultrasonic methods. The effect of porosity and cross-section thickness in diecast AZ91 was also assessed. Coarse-grained pure Mg and fine-grained Mg–0.3Zr have similar elastic moduli. The modulus increases then decreases with increasing content of Al or Zn in solid solution, with a maximum value at an electron concentration of ca. 2.01. The modulus of aged sand-cast AZ91 specimens increases with the volume fraction of β-Al₁₂Mg₁₇ precipitates. The cross-section thickness seems to have no influence on the modulus of die cast material, but it decreases with the porosity content. An elastic modulus chart was constructed for AZ91 alloy accounting for the possible effects of solute in solution, volume fraction of precipitates and porosity content.