A comparison of uniaxial and multiaxial non-proportional fatigue properties in cast Al-Si-Cu-T6 alloys solidified at two cooling rates: Fatigue behavior, fracture characteristics and dislocation evolution

Abstract

The cyclic deformation behavior and fatigue fracture characteristics of cast Al-Si-Cu-T6 (A319-T6) alloys solidified at two cooling rates under uniaxial and multiaxial non-proportional loading conditions were investigated. The A319-T6 alloy exhibited cyclic hardening and additional non-proportional hardening effects during cyclic loading. The cyclic hardening rate and non-proportional loading sensitivity coefficient improved by 2.8% and 5.1%, respectively, when the solidification cooling rate was increased from 0.1 to 10 °C/s. To account for the hardening effects, the dislocation evolution and interaction between dislocations and other microstructures were analyzed. Based on the asymmetry parameter, the tension-compression symmetries of A319-T6 alloys subjected to uniaxial and multiaxial non-proportional loading were discussed. The presence or absence of a steady crack propagation area was considered to be the primary difference in the cross-section caused by cooling rates, leading to varied fracture flatness. Multiaxial non-proportional loading yielded reciprocating wear marks and a significant quantity of wear debris on the fracture surface. The majority of wear debris was identified as matrix oxide. The reciprocating wear process removed fatigue striation and secondary cracks that emerged on the uniaxial fracture, further increasing fracture flatness.