Thermo-mechanical fatigue property of a surface-hardened AC4CH cast aluminum alloy

Abstract

The thermo-mechanical fatigue life and microstructural change under a compression-tension thermo-mechanical cyclic loading of a surface-hardened Al-Si-Mg alloy casting are investigated. A surface cold working technique using steel balls is utilized for the surface hardening. Out-of-phase type thermo-mechanical fatigue tests have been performed with the temperature range of 323–523 K and the applied mechanical strain range of 0.75–2.0%. The surface-hardened material exhibits better thermo-mechanical fatigue property especially in a low cycle regime, together with higher generated stress, suggesting that it is even superior under stress-controlled loading. The differences in the stress–strain hysteresis loops and hardness variation near specimen surface between the materials with and without surface hardening have not vanished until final fracture. The observed difference in the thermo-mechanical property is attributed to some microstructural differences. The effects of damaging at the silicon particles to this difference are also investigated using the high-resolution microtomography technique. It has been clarified by microstructural observations that recovery and recrystallization are suppressed in the surface-hardened material. It can be inferred that such thermal stability is attributed to the multi-axial deformation by a combination of the surface hardening and the thermo-mechanical loading.