Influence of Solidification Rates and Stress-Relief Annealing on the Mechanical Properties of Cast 6063 Aluminium Alloy

Abstract

This paper reports the influence of solidification rate and stress-relief annealing on the mechanical properties of cast 6063 Aluminium alloy (Al6063). Ingots of Al6063 were melted and then cast using sand and metal moulds. Some of the cast samples were heat treated and then cooled in natural air. Tensile test, hardness test, impact test and microstructural analysis were carried out on the samples. The results show substantial changes in the mechanical properties of the specimens. The ultimate tensile strength, yield strength and hardness percentage elongation of cast Al6063 increases with the use of casting method with high thermal conductivity and reduces when annealing is carried out on the specimens. The ultimate tensile strength of 146.7 MPa and 163.5 MPa were recorded for sand mould and metal mould samples, respectively and the values decreases by 10.3% and 7.5% for the respective moulds. In contrast, the values of impact strength and percentage elongation of cast Al6063 rod improved with the increase in thermal conductivity of casting method and annealing operation. The ductile increased by 51.01% and 45.82% for sand mould and metal mould samples, respectively, after they were annealed. Furthermore, microstructural analysis of cast Al6063 rod revealed a fine-grained structure with increase in thermal conductivity of casting method used; however, the annealing process encouraged grain growth as a result of the stress being relieved from the samples.

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“…These properties can be improved using mould with high thermal conductivity. Also, Stephen et al [7] and Isadare et al [9] showed the heat treatment (stress relief annealing) improved impact strength and ductility of cast aluminium alloy.…”

“…luminium is the most widely used non-ferrous metal for engineering applications due to its unique combination of properties; good corrosion resistance, high strength stiffness to weight ratio, good electrical and thermal conductivities, and prospects of recycling at low energy costs [1][2][3]. The properties of aluminium are normally improved by addition of alloying elements, manufacturing techniques and heat treatment [4][5][6][7][8]. Aluminium is often strenghtened by reinforcement with particles and fibres via casting (to obtain metal matrix composite) or with windings of resinimpregnated fibre strands (filaments) on its surface.…”

“…Many investigations have studied the effects of casting techniques and post-cast heat treatment schedules on cast aluminium alloys in order to improve strengths and provide acceptable ductility [7,9,10,11,12]. Typical heat treatment methods to which aluminium are subjected are solution heat treatment and stress relief annealing.…”