Aging Time on the Microstructure and Mechanical Properties of A356 Alloy by Semi-solid Processing

Abstract

An investigation was carried out to study the effects of aging time on the microstructure and mechanical properties of A356 alloy by semi-solid processing. The alloy was subjected to solution treatment for 4 h at 540 °C, artificial ageing was carried out at temperature (170 °C) and different time (0–24 h). The results revealed that the needle-shaped eutectic Si phase in as-cast ingot was transformed to globular shape compared with that by solution treatment. Meanwhile the Chinese script π-Fe(AlMgSiFe) phase was transformed to smaller and uniformly distributed β-Fe(AlFeSi) phase, the elongation increased obviously. With the increasing of aging time, the elongation decreased, and the ultimate tensile strength increased. When the aging time was 4 h, the alloy achieved the optimal mechanical properties. The micro-hardness was 121HV, ultimate tensile strength was 329 MPa, and the elongation was 15%. From the fracture morphology, the fracture for alloy aging for 4 h showed more dimples. With the increasing of aging time, the ultimate tensile strength and the elongation decreased.