Papers by Keyword: SIMA Process

Abstract: Effects of SIMA processing on size and shape of primary solid particles of Cu34wt.%Zn2wt.%Pb brass alloy was investigated. The optimal temperature for semisolid processing of the alloy was found to be around 890 °C using Thermo-calc simulation software. Liquid fraction sensitivity of the alloy around this temperature is 0.012. The results indicated the formation of non-dendritic microstructure even after 1 min holding of 10% cold worked sample at 890 °C. Sphericity of the primary solid particles increased by increasing the cold working ratio and holding time. The smallest size (103 μm) and highest shape factor (0.84) of the primary solid particles were achieved at 30% cold working ratio and 5 min holding time.

Abstract: In current research the effect of the strain-induced melt activation (SIMA) process on the microstructure of 6061 Al alloy has been investigated. The optimum amount of Ti for proper grain refining was found to be 0.03 wt.% in the alloy. In SIMA process, after hydraulic pressing, recrystallization and partial melting (RAP) were employed to obtain a fine globular microstructure. Certain amount of strain (40%), heat treatment time (30 min) and temperatures (605-645^°C) were employed to find an optimized fine globular microstructure of the alloy. A microstructural study which was carried out by optical microscopy, exhibited the uniform equiaxed recrystallized grain structure.

Abstract: Forming in semi-solid state to achieve globular microstructure has an effective influence on mechanical properties of aluminum alloys. In this research, the Al2014 alloy was prepared by a semi-solid strain-induced melt activated (SIMA) process. In order to analyze the effect of titanium content on the macrostructure of Al2014, the optimum amount of titanium according to its efficiency on reducing the grain size was obtained. Then, specimens with optimum titanium content were prepared by the SIMA process. Cold working was applied on specimens by an upsetting technique. Cold worked specimens were heat treated at 595, 605, 615, 625 and 635°C and were kept at these temperatures for 30 min to achieve a globular structure. Observations through optical and scanning electron microscopy (SEM) revealed that by increasing the temperature, an increase in sphericity and grain size occurs. According to the results, optimum condition in order to achieve a fine and globular microstructure is keeping specimens at 625°C for 30 min.

Abstract: The effects of isothermal temperature on the microstructure evolution of semisolid A6070 alloy produced by strain-induced melt activation process were investigated. The results showed that high semisolid isothermal temperature could make the semisolid particles more globular, but the size of the particles would grow larger and accelerate the spherical evolution of the solid particles. It was found that the optimal process temperature should be 620 °C and 10 min of isothermal temperature based on the conditions of this paper.

Abstract: In this study, in order to compare effect of unidirectional compression and rolling on final microstructure of strain induced melt activated (SIMA) A356 aluminum alloy, rectangular samples with dimensions of 3cm×5cm in area and 1cm in thickness and cylindrical specimens with 2.5cm in diameter and 1cm in length, have been prepared for rolling and compressing processes, respectively. Then, these samples were plastically deformed at a same strain in ambient temperature. Afterward, the strained samples were cut into equal quarters. In the next stage, to produce globular microstructure, these specimens were partially remelted in 580°C for different times. Results obtained from light microscopy showed that specimen's thickness and so, its strain affected zones influence on the globulization of dendrites. In addition, it was seen that at a given strain and constant diameter, increase of H/D ratio led to increase of needed time for reaching a certain sphericity in cylindrical samples. Also, it was showed that microstructural evolutions during SIMA processing of both rolled and unidirectional compressed samples were relatively identical. However, at a same condition, ultimate size of globulized dendrites in the rolled samples was smaller than those of compressed ones.

Abstract: Thixoforming offers the possibility of forming complex aluminum parts with a superior quality and a reduction of processing steps. The production of a fine, equiaxed, globular microstructure is essential for thixoforming. Strain Induced Melt Activation (SIMA) and the Cooling Slope (CS) casting processes were employed to produce AA6082 thixotropic feedstock in the present work.. SIMA process produces such a microstructure through recrystallization of heavily deformed billets and a subsequent heat treatment in the mushy zone. Molten metal with a suitable superheat is cast over a water-cooled, inclined metal plate into a permanent mould to produce the thixotropic billet in the CS casting route. The effect of cold work and heating temperature and time were investigated for the SIMA process where as the effect of CS length, casting temperature on the final microstructures were investigated for a fixed set of heating conditions in the CS casting route.