High-temperature load retention behavior of general-purpose wrought magnesium alloys

Stress relaxation behavior of general-purpose wrought Mg-3Al-1Zn (mass%, AZ31) alloy was investigated by bolt load retention test. Rolled AZ31 alloy sheets, which had high density of dislocations and fine grain structure, showed large stress drop during the test, presumably owing to the enhanced dynamic recrystallization or grain boundary sliding. Unlike the rolled samples, an extruded AZ31 alloy had coarse-grained recrystallized microstructure, resulting in the relatively low stress drop during the test. For comparison, the stress relaxation behavior of a commercial rolled Al-Mg alloy (A5052-H34) sheet was evaluated. Although high density of dislocations existed in the aluminum sheet, dynamic recovery and dynamic recrystallization were suppressed, which led to the limited stress drop during the test.