The effects of quenching rate after a solution treatment on strength and fracture toughness of a 6061 aluminum alloy have been investigated, varying the width of PFZ layer and coarse secondary phase particles at grain boundaries by changing the quenching rate utilizing both water quenching and air-cooling. In-situ observation of the fracture toughness tests was also performed to investigate the effects of such microstructural parameters on crack initiation and propagation behaviors. By decreasing the quenching rate, the width of the PFZ layer increases from about 40 to 310 nm, and density and size of the coarse particles increase at the grain boundaries. Mechanical properties such as tensile strength, 0.2% proof stress, elongation, fracture toughness and crack propagation resistance are decreased simultaneously. Especially, the effects of quenching rate on the strength and the crack propagation resistance are remarkable. Such degradation of the mechanical properties is attributed to expansion of the PFZ layer with decreases in quenching rate. It causes localization of plastic deformation, and consequently, transition of fracture mechanisms from grain interior ductile fracture to grain boundary ductile fracture at the PFZ layers. In-situ SEM observation reveals that the effects of the coarse particles at grain boundaries are much less effective than those of the PFZ.
|ジャーナル||Keikinzoku/Journal of Japan Institute of Light Metals|
|出版ステータス||出版済み - 1 1 2001|
All Science Journal Classification (ASJC) codes