Effect of Mg_(17)Al_(12) precipitates on the microstructural changes and mechanical properties of hot compressed AZ91 magnesium alloy

摘要

During hot compression, Mg_(17)Al_(12) (β) precipitates show strong influence on the microstructural changes of 415℃-24h homogenized AZ91 alloy. When compressed at 300℃ and 350 ℃, dynamic recrystalliza-tion (DRX) only occurs near grain boundaries with discontinuous β precipitate pinning at the newly DRXed grain boundaries. With increasing compression temperature and decreasing strain rate, the β-precipitating region expands; however, the amount of pinning precipitates decreases, resulting in increases in the DRX ratio and average DRXed grain size. With a compression ratio of only 50%, the specimen compressed at 350 ℃ and a strain rate of 0.2 s~(-1) (designated 350 ℃-0.2 s~(-1) compressed specimen) shows an ultimate tensile strength (UTS) of 334 MPa, a 0.2% proof stress (PS) of 195 MPa and an enough elongation of 17.9%. After a subsequent aging treatment at 180 ℃, due to the large number of p precipitates, the strength of the compressed specimens are further improved, and the specimen peak aged after compression at 400 ℃ and 0.2 s~(-1) shows UTS of 364 MPa and PS of 248 MPa with a moderate elongation of 7.7%.