Microstructure and Mechanical Properties of Severely Deformed Eutectic Al-Si-Cu-Mn Alloy

In this study, the microstructure and mechanical properties of severely deformed Al-12Si-3Cu-0.5Mn alloy were systematically investigated. The alloy produced by permanent mold casting was homogenized and processed with multi-direction forging (MDF) up to four cycles at 200 degrees C. MDF gave rise to fragmentation of hard particles, formation of dispersoids, and fine grains with high angle grain boundaries. The grain size of the alloy after one-cycle MDF decreased from 27.30 mu m to sub-micron levels of about 0.5 mu m. After one-cycle MDF, the formed microstructure consisted of ultrafine grains (UFG) with and without intense dislocations. Lattice microstrains and dislocation densities of the alloy decreased with increasing forging cycles. In general, hardness, yield and tensile strength, elongation and impact toughness of the alloy increased after MDF. The highest hardness, yield and tensile strength of the alloy were obtained after the two-cycle MDF, while the four-cycle MDF produced the highest elongation and impact toughness values. Fracture surface of the tensile tested alloy before MDF consisted of large cleavage planes and hills. However, narrow cleavage planes and plenty of dimples occurred on the tensile fracture surface of the alloy after MDF. These findings were elucidated according to microstructural alterations as a result of fragmentation of hard particles, formation of dispersoids and fine grains, annihilation of dislocations and grain growth.