Effects of Rheocasting and Thixoforming on the Microstructure and Mechanical Properties of A356 Aluminium Alloy

Abstract

This paper presents the changes in mechanical properties and microstructure of aluminium alloy A356 that undergoes cooling slope casting. The alloy was cut into small cubes with an estimated weight of 400g before it was heated in a crucible induction casting machine. The temperature was set to 880 oC with a heating rate of 15 oC per min. Then, the metal was cooled to 620 oC until it turns to a semisolid, before pouring into a stainless steel mould through a 250 mm long and 60o cooling slope before it was cooled to room temperature. For the thixoforming experiments, the liquid fraction was between 30% and 50%, with various semisolid temperatures (583 oC-585 oC). The ram speed and die temperature were 85 mm/s and 200 oC, respectively. The microstructure and mechanical properties of rheocast feedstock in T6 condition were determined and compared with the metal without any heat treatment, rheocast and thixoformed alloy. It was found that thixoformed metal had the highest ultimate tensile and yield strength with reduced ductility. The microstructures are rosette, near globular and spherical, and were obtained in rheocast and thixoformed alloys, respectively. The α-Al grains were larger at higher semisolid temperatures.

Microstructural Evaluation and Corrosion Resistance of Semisolid Cast A356 Alloy Processed by Equal Channel Angular Pressing

“…Using a graphite crucible, the as-cast was melted at a temperature of 750 • C. For the cooling slope casting process, the cooling slope of stainless steel, with a slope length of 250 mm as well as a tilt angle of 60 • , was used. The reason for selecting these conditions was based on our work [31]. The apparatus used for this process is shown in Figure 1a.…”

“…The apparatus used for this process is shown in Figure 1a. This study specifically selected 620 • C as the pouring temperature to limit the superheating of the melt [31]. The molten metal was poured downward, on a stainless steel slope, into a mold with a vertical surface, before quenching in water.…”

The Microstructural Refinement of the A356 Alloy Using Semi-Solid and Severe Plastic-Deformation Processing

“…A mould for the molten alloy was positioned at the bottom of the cooling-slope plate, where it was quenched immediately in water at room temperature. Both the as-cast and cooling-slope samples were subjected to T6 thermal treatment in this study, involving the following procedures: (1) solution treatment at 540 • C for 8-h, (2) rapid quenching in water, and (3) ageing treatment at 180 • C for 3-h [21]. Following that, using an electrical discharge machine (EDM), the as-cast and cooling-slope samples were machined to a 10 mm diameter with a 1 mm thickness for microstructure analysis and hardness testing.…”