Strain Induced Melt Activation Process Research Articles

Effect of predeformation on the globular grains in AZ91D alloy during strain induced melt activation (SIMA) process

The effect of predeformation on the α-Mg grains in the AZ91D alloys was investigated in different stages during the semisolid processing. The result showed that, with the increase of compressive ratio, the α-Mg dendrites in the as-cast microstructures gradually oriented themselves in the direction that was vertical to the compressive direction, and exhibited an obvious directional character. During the sequent heat treatment at 310 °C for 20 min, the recrystallization was induced in the deformed alloys by the increasingly accumulated systemic strain energy. The metallographical observation showed that the average size of recrystal α-Mg grains gradually reduced with the increase of compressive ratio. The reason might be that the nucleation to growth ratio of the renascent recrystal α-Mg grains gradually increased in the recrystallization process. Due to the recrystallization mechanism, the predeformation made the α-Mg grains particularly rounder and finer after the semisolid isothermal heat treatment at 560 °C for 20 min. The average diameter of the globular α-Mg grains in the semisolid microstructures also reduced with the increase of compressive ratio and this descending trend was almost similar to that in the recrystal microstructures, which further demonstrated that the recrystallization had an inevitable role on the evolution process of globular grains during SIMA process. While the compressive ratio surpassed 20%, the above descending trend was not so evident as that below 20%. In addition, the effect of predeformation on the tensile strength and elongation of the semisolid AZ91D alloys was also discussed in the present paper.

Grain growth of Al-4Cu-Mg alloy during isothermal heat treatment

Abstract The microstructure of an Al-4Cu-Mg alloy during isothermal heat treatment in the Strain Induced Melt Activation (SIMA) process was investigated and the kinetics of grain growth was analyzed. The grain growth during isothermal heat treatment of the Al-4Cu-Mg alloy coincided with the Ostwald ripening theory. During isothermal heat treatment, both grain shape and the high volume fraction of solid phase have significant effects on grain growth. Therefore, a new grain growth model based on the Ostwald ripening theory was proposed taking into consideration the grain shape and the volume fraction of solid phase. By comparing the calculated results with the experimental results, it was confirmed that the present model could be applied to grain growth during isothermal heat treatment of the Al-4Cu-Mg alloy in the SIMA process.

Mechanical properties and microstructural evaluation of AA5013 aluminum alloy treated in the semi-solid state by SIMA process

The microstructure and mechanical properties of AA5013 aluminum alloys prepared by strain-induced melt activation (SIMA) process were studied to investigate the effects of cold working and heat treatment conditions. The specimens subjected to deformation ratios of 30 and 50% and various heat treatment time and temperature regimes were characterized in the present study. The results revealed that for the desired microstructure of the alloy, the optimum heat treatment temperature and time were 650 °C and 60 min, respectively, for both deformation ratios. However, the specimens with 50% cold working exhibited more brittle behavior while they contain finer grains with uniform distribution along the cross-sections as compared to 30% cold working.

Fabrication and Microstructure Evolution of Semi-Solid LY11 Alloy by SIMA

For semi-solid metal forming, it is essential to fabricate the semi-solid materials with spheroidal microstructure. Among several fabrication techniques of the semi-solid materials, (strain-induced melt activation (SIMA) is an ideal candidate with the advantages of simplicity and low equipment costs. In this paper, the microstructure evolution of LY11 alloy (approximately corresponding to ASTM 2017) was investigated in the SIMA process, which had two essential stages: deformation and isothermal heat treatment. The deformation stage was conducted using a CSS-1100C material testing machine and the isothermal heat treatment stage was performed in a resistance furnace. Different levels of deformation temperatures, ram velocities, isothermal temperatures, and holding times were used in this investigation. The microstructure of LY11 alloy was observed by a NEOPHOT-1 optical microscope. The results indicated that the processing parameters must be selected properly to obtain the fine, uniform and spheroidal microstructure by SIMA. The deformation-recrystallization mechanism for microstructure evolution in SIMA process was supported by experimental evidence.