Influence of Grain Refinement by Al-5Ti-1B on the Microstructure and Mechanical Properties of Aluminium Alloy A356

الملخص

An investigation was carried out to understand the effect of grain refinement on the microstructure and mechanical properties of Al-alloy A356 by addition of varying weight percentage of Al-5Ti-1B. Grain refinement and modification of α- phase in Al-Si alloys are considered as important task resulting from solidification process. Two different approaches to grain refinement by solidification process have been pursued physically induced and chemically stimulated. The physical relies mainly on the use of external field, such as ultrasonic vibration, while the chemical approach depends primarily on addition of grain refiner, which is the subject of this research work. The effect of grain refiner on the solidification of the A356 alloy was studying and the obtained samples were characterized by optical microscopy. The mechanical properties (σuts, σ0.2 and δ) of the refined A356 alloys were investigated as a function of the addition level of Al-Ti-B master alloy (0, 1, 3,5 wt.%). The results indicated that the primary α- phase aluminium are significantly refined and the microstructures changed from coarse dendrites to fine equiaxed α-Al dendrites, without any change in the morphology of the eutectic Si particles. Additionally, the tensile strength, yield strength and elongation are increased noticeably with addition of grain refinement. The tensile strength, yield strength and elongation of the A356 with 3 wt % grain refine of (Al -5Ti- 1B) are 156.3 MPa, 104.3 MPa and 4.9%, i. e., the percentage of improvement was 12 %, 6 % and 8.9 %, respectively.