Microstructure and Mechanical Properties of Mg Alloy Sheets Produced by Twin Roll Caster

摘要

Mg-Al-Zn alloys containing 0.5% Ca were strip cast into sheets with a thickness of about 1.0mm by twin roll caster. It is found that the addition of Ca to Mg_(95)Al_(5-X)Zn_X (wt%)alloys prevents the oxidation and burning of molten, and makes the melting and casting easy. The as-cast Mg_(96)Al_4Zn_(0.5)Ca_(0.5) alloy sheet has few cracks at the edge. With increasing Zn content, the generation of cracks occurs more markedly. The as-cast alloys have equiaxed grains with an average grain size of 10 urn. A fine microstructure is obtained. All the samples consist of single hcp-Mg phase. The yield and ultimate tensile strength of the as-cast sheets are in the range of 180 to 200 Mpa and 265 to 275 Mpa, respectively. The alloy Mg_(95)Al_2Zn_(2.5)Ca_(0.5) shows an elongation of 21% as well as a high strength of 275 Mpa. The annealing at 400 ℃ causes an improvement of elongation to 24% and 30% for Mg_(96)Al_4Zn_(0.5)Ca_(0.5) and Mg_(95)Al_2Zn_(2.5)Ca_(.5),respectively. A further enhancement of mechanical properties is expected by an appropriate thermomechanical treatment. The as-cast Mg_(96)Al_4Zn_(0.5)Ca_(0.5) sheet was deep drawn at 250℃ and a drawing ratio of 2.0 without cracking . In summery, the Ca added Mg alloys are suitable for the production of Mg alloy sheets by strip casting and the cast alloy sheet have high strength with ductility and good formability.