Effects of Process Parameters on Microstructure and Mechanical Properties of Semi-Solid Al-7Si-0.5Mg Aluminum Alloy by Gas Induced Semi-Solid Process

Abstract

Al-7Si-0.5Mg aluminum alloy semi-solid slurry with good spherical grains was prepared by gas induced semi-solid process (GISS) and the effects of both holding time and medium alloy addition on the microstructure of the semi-solid slurry were investigated. These two parameters have a great influence on the solid fraction, the size and the sphericity of the grains. With holding time increased from 85 s to 270 s, the solid phase fraction of the semi-solid slurry decreased from ~0.77 to ~0.67, the average grain size increased from ~95 μm to ~225 μm and the average shape factor decreased from ~0.80 to ~0.33. When medium alloy addition varied in the range of 0.5–2.0 wt%, a better slurry microstructure was obtained at about 1.5 wt%. Compared with the conventional liquid die-casting, the semi-solid die-casting improved the mechanical properties of tensile bars; yield strength, tensile strength and elongation of tensile bars reached ~240 MPa, ~307 MPa and ~8.8% after heat treatment, respectively. In conclusion, GISS process can prepare the semi-solid slurry with uniform and round microstructure, and the semi-solid die-casting can improve mechanical properties of Al-7Si-0.5Mg aluminum alloy.

Microstructure, Segregation and Mechanical Properties of A356 Alloy Components Fabricated by Rheo-Hpdc Combined with the Swirled Enthalpy Equilibration Device (Seed) Process

“…The procedure for the estimations was detailed in Ref. [18]. In addition, point counting method (GB/T 15749-2008) was used to obtain static results of the Ferich intermetallic compounds.…”

A Comparative Study on Microstructure, Segregation, and Mechanical Properties of Al-Si-Mg Alloy Parts Processed by GISS-HPDC and SEED-HPDC

“…The solid fraction (Fs) was estimated by measuring the volume fraction of the large light gray α-Al grains, which were preserved during quenching from a semi-solid state. The detailed procedure for the measurement is given in [17]. During the quantitative image analysis, at least 300 grains for the same sample were measured.…”

“…Additionally, GISS involves a longer holding time, which contributes to larger α 1 -Al grains. Tang [19] observed a significant decrease in the average grain size with an increasing cooling rate, while Gu [17] discovered that the grains grew and even developed dendritic structures through the Oswald ripening mechanism with prolonged resting time.…”