Microstructure and mechanical properties of thixoformed A319 aluminium alloy

• Published in: Materials in engineering Vol. 64; pp. 142 - 152
• Main Authors: Salleh, M.S., Omar, M.Z., Syarif, J., Alhawari, K.S., Mohammed, M.N.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2014
• Subjects: Aluminium alloy; Cooling slope casting; T6 heat treatment; Thixoforming; Aluminium alloy; T6 heat treatment; Cooling slope casting; Thixoforming
• ISSN: 0261-3069
• DOI: 10.1016/j.matdes.2014.07.014

•A319 was successfully thixoformed at 50% liquid, i.e. at 571°C.•T6 heat treatment has increased the strength and hardness of the thixoformed alloy.•The elongation after T6 heat treatment is even significantly improved.•The iron-rich intermetallic phase reduces the strength of the thixoformed alloy. Thixoforming is a viable technology for forming alloys in a semisolid state into near net-shaped products. In the present study, the effect of a thixoforming process on the microstructure and mechanical properties of A319 aluminium alloy was investigated. The ingots obtained from the cooling slope were thixoformed in a press after they remained at 571°C for 5min, yielding a microstructure predominantly composed of α-Al globules and inter-globular Si particles. Some of the thixoformed samples were treated with an ageing process (T6) and then, hardness and tensile samples were prepared from the as-cast, as-thixoformed and thixoformed T6. All the thixoformed samples were characterised using optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) as well as hardness measurements and tensile tests. The results indicate that the mechanical properties of the thixoformed A319 alloy increased after the T6 heat treatment (hardness of 124.2±3.2 HV, tensile strength of 298±3.0MPa, yield strength of 201±2.6MPa and elongation to fracture of 4.5±0.3%). The fracture samples from the tensile test were analysed, revealing that the iron-rich intermetallic observed in the samples reduced the tensile strength and ductility of the thixoformed A319 alloys.