The Effect Of Alloy Element And Cryogenic Treatment On Al-Si Alloy Mcchanical Properties And Microstructure

Hypoeutecic Al-Si alloy has many advantages such as small proportion, high specificstrength and good machining performation. In recent years, the use of the aluminum alloygrows greatly in transportation. There is a huge development potential in the industrialproduction.This paper investigates hypoeutecic Al-Si alloy, studys the mechanical properties andmicrostructure affected by trace element Zn and Ag. The result showed that Zn can refineAl-Si-Cu-Mg alloy as-cast microstructure a little, but the effect of it islimited. After T6heattreatment, with the Zn content increased, the tensile strength and elongation declined after arise first, when the Zn addition rose to0.75%, the tensile strength and elongation reached339MPa and4.5%respectively. The strengthening mechanism is Zn distributed in the matrixevently as a substitutional solid solution form, leading to the lattice distortion degree biggerand hinder the dislocation, so the mechical properties of the alloy improved. The study alsofound that the addition of Ag reached0.4%, the tensile strength and elongation of T6heattreatment alloy reached to298MPa and5.3%. Ag distributed in the matrix evently after adding0.6%.This paper also studies the effect of Zn on the low temperature mechanical properties ofAl-Si-Cu-Mg alloy. The result showed the addition of Zn increase properties compared with0%Zn alloy, and the tensile strength reached to330MPa, increased by6.5%, compared to0%Zn alloy when the temperature arrived at-60℃, as well as the elongation reached to3.4%,increased by14.5%. Therefore, Zn can improves the low temperature properties ofAl-Si-Cu-Mg alloy.Through the study of cryogenic treatment, we found this method can increase the tensilestrength and hardness, reduce the elongation significantly. After changing the liquid nitrogenholding time, we foung that the tensile strength reached to338.2MPa after a treatment of525℃(8h)+cryogenic treatment for24h+165℃(6h), and the elongation reached to2.4%,declined42.9%compared with T6treatment. During cryogenic treatment, the second phaseprecipitated rapidly with the decline of the temperature, and the number of precipitationincreased. At the same time, the alloy volume contracted, the lattice narrowed, so the compressive stress was generated in the organization not only leadind tiny crystal produced,achieving the effect of refining grains, which improves performance of the alloy.