Tensile properties of forged direct-squeeze-cast Al-(6.0-8.0 mass %)Si-(0.3-0.52 mass %)Mg alloy

The effects of lubricants on the quality of squeeze-cast Al-(6.0-8.0 mass%)Si-(0.3-0.52 mass%)Mg alloys were studied. Different melts with varying amounts of Si and Mg were prepared and then directly squeeze-cast into cakes. Different lubricants and two different pressures, 60 and 120MPa, were used in the production of the cakes. These squeeze-cast cakes were then forged and heat-treated. Tensile specimens prepared from the forged and heat-treated cakes were tested to determine their tensile properties. Among all the variables tested, the Weibull modulus (in ultimate tensile strength, UTS) was the largest (m = 53.7) for the cakes squeeze-cast at 120MPa using water-based BN powder (∼4 μm in size) as a lubricant. After polishing and ultrasonic-vibration treatment, oxide films appeared as foggy films on the chilled blocks and forged cakes. Reaction films were also observed on the tensile fracture surfaces of the tested bars. They were particularly apparent on the bars produced from cakes that had been prepared using an oil-based lubricant. The area ratios of the foggy films and reaction films on the samples were calculated. The Weibull modulus (in UTS) of the forged cakes after T6 treatment was significantly affected by both the pore count and the total area ratio covered by reaction films and foggy films.