Análise do tratamento térmico (T6) na liga Al-7,5si-0,5mg solidificada sob pressão: microestrutura e microdureza

Abstract

Squeezing casting is a process where molten metal solidifies under pressure. Parts produced by this method generally have fine and almost fully equiaxial granulation compared to conventional die casting. The good mechanical properties obtained by squeeze casting are due to the microstructure, since the dendrites and interdendritic spacing of pressure solidified parts are smaller than those cast in the absence of pressure. Several alloys can be manufactured by this method, among them stands out the Al-Si alloys which, due to their good fluidity, facilitates the instant filling of the mold. The addition of Mg to this system (Al-Si) allows hardening through the T6 heat treatment, allowing to obtain a lightweight material with good mechanical properties, such as high hardness values. Al-Si-Mg system alloys are widely used in the automotive and aerospace industries, being applied in the manufacture of wheels, chassis, suspension, among others. The objective of this work is to analyze the influence of T6 heat treatment on the microstructure and microhardness of Al-7,5Si-0,5Mg alloy produced through the squeeze casting process. Correlating the influence of pressures with secondary dendritic spacing and variations in Vickers microhardness. For this, ambient pressures of 50 MPa, 100 MPa and 150 MPa were used. In general, it was observed that the heat treatment influenced the modification of the silicon morphology and the increase of Vickers microhardness. Secondary dendritic spacing increased to positions farther from the metal / mold interface in the alloy prior to heat treatment. It was also noted the influence of pressure on the reduction of secondary dendritic spacing and increased microhardness Vickers.