Forging Condition for Removing Porosities in the Hybrid Casting and Forging Process of 7075 Aluminum Alloy Casting

In this study, the ranges of compression ratio for the successful implementation of hybrid casting and forging process for 7075 aluminum alloy are investigated. Hybrid casting and forging process combines the advantages of casting and forging processes. In this process, a near net shape preform is first cast and the casting is subsequently forged. The casting defects such as shrinkage porosity can be eliminated by forging and the number of forging steps can also be reduced. Therefore, the production cost can be reduced. In this study, castings with stepwise cross section are die cast with 7075 aluminum alloy. The stepwise cross section has three different thicknesses, which are 15 mm, 10 mm and 5 mm. The aim of this study is to obtain how high compression ratio is required to eliminate the porosities inside the preform castings with various thicknesses, where porosity contents are different, and what are the maximum compression ratios that can be tolerated before these preform castings fail. These data are crucial to the design of the preform casting for the hybrid casting and forging process. The experimental results show that for 7075 aluminum alloy, it requires a compression ratio of 30% to eliminate all the porosities in the casting section of 5 mm in thickness and a maximum compression ratio of 44% can be tolerated. For the casting section of 10 mm in thickness, it requires 41% of compression ratio to eliminate all the porosities and a maximum compression ratio of 64% can be tolerated. For the casting section of 15 mm in thickness, it requires 52% of compression ratio to eliminate all the porosities and a maximum compression ratio of 64% can be tolerated.