Influences of Al2.5Cu0.5Ti master alloy on micro-structure and mechanical properties of Al-7Si alloy

Abstract

The influences of adding Al2.5Cu0.5Ti master alloy (0.3%, 0.5%, 0.7%, 0.9% and 1.3%, mass fraction, the same below) prepared by vacuum arc melting furnace with a water-cooled copper mold on the microstructure and mechanical properties of Al-7Si alloy were investigated by optical microscopy (OM), scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), X-ray diffractometer (XRD), differential scanning calorimeter (DSC) and tensile testing machine. The results show that the primary α-Al and eutectic Si structure of Al-7Si alloy with Al2.5Cu0.5Ti master alloy addition are significantly refined.Compared with the unadded Al2.5Cu0.5Ti master alloy, when the addition concentration of Al2.5Cu0.5Ti master alloy is up to 0.9%, the primary α-Al is refined from coarse dendrites to fine equiaxed dendrites and the size reduces from 218 μm to 80 μm, the second dendrite arm spacing (SDAS) significantly decreases from 25 μm to 9.3 μm.The morphology of eutectic Si is transformed from coarse needle/flake to short flake and rod. The length of eutectic Si structure reduces from 34.8 μm to 11.6 μm, and the width decreases from 4 μm to 1.7 μm. The tensile test indicates that when the addition content of Al2.5Cu0.5Ti master alloy is up to 0.9%, the ultimate tensile strength (UTS) is increased by 13.6% from 162 MPa to 184 MPa, and the elongation (El) is enhanced by 210% from 3% to 9.3%. The fracture mode of the alloy changes from ductile-brittle mixed fracture to ductile fracture mode.However, when the addition content of Al2.5Cu0.5Ti alloy increases to 1.3%, excessive modification occurs, resulting in coarsening of the microstructure and decrease in mechanical properties.

Keywords

• al-7si alloy
• al2.5cu0.5ti master alloy
• primary α-al
• eutectic si
• mechanical property