Semi-Solid Slurry Casting Using Gas Induced Semi-Solid Technique to Enhance the Microstructural Characteristics of Al-4.3Cu Alloy

Semi-solid processing of Al-4.3%Cu (A206) alloy was performed by Gas Induced Semi-Solid (GISS) process in different condition. The flow rate of argon gas, starting temperature for gas purging (the temperature of superheated-melt) and the duration of gas purging were three key process variables which were changed during this investigation. It was found that inert gas purging near liquidus, significantly, led to the microstructural modification from fully dendritic to globular structure. Thermal analysis was successfully implemented through CA-CCTA technique to understand the cause of the microstructure change during GISS process. The results showed that gas purging into the melt leads to temperature drop of the melt to its liquidus just after a few seconds from start of gas purging. In fact, copious nucleation was induced by cooling effect of inert gas bubbles. Microstructural features were characterized in semi-solid as well as on conventionally cast samples. The optimum gas purging temperature, injection time, and inert gas flow rate was determined in semi-solid processing to obtain the best globularity in the microstructure of a long freezing range alloy. However, the microstructure of the conventionally cast sample was fully dendritic with shrinkage which affects the soundness of casting products.

Enhanced Mechanical Properties of A206 Aluminum Casting Alloy by Addition of Rare Earth Elements

Changes in tensile properties of A206 Al-Cu-Mg casting alloys containing trace amount of rare earth(RE) elements up to 0.2% were investigated and discussed in relation to the microstructural evolution. The A206 alloy with 0.1%RE shows higher values of ultimate tensile strength(UTS) and yield strength(YS) than A206 alloy at room and elevated temperatures up to 300oC, whereas no remarkable change is found in elongation with respect to RE addition. In view of X-ray diffractometry(XRD) and transmission electron microscopy(TEM), the improvement of tensile strength in the A206 alloy with 0.1%RE would be caused by higher number density of Al2Cu(q¢) strengthening precipitates.