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Isothermal Multi-Axial Forging Characteristics of Mg-3%Al-1%Zn Alloy for Aerospace Structural Applications

T Ram Prabhu

In the present study, the AZ 31B Mg alloy was isothermally upsetted by multi axial forging. Two increasing temperatures (350°C and 400°C) and working ratios (0.3 and 0.4 per direction) were selected as variables in the multi axial forging. The forging operation was performed in a 10000 kN industrial hydraulic press at a forging speed of 33.3 mm/s. The grain structure and microstructure of the forged alloy were investigated using an optical microscope. The hardness measurements were taken and correlated with the grain size of the alloy. The key findings from the present investigation are: (1) the grain refinement can be retained by decreasing the forging temperature (350°C) and the reduction ratio (0.3 per direction), (2) increasing working ratio favours the preferential grain growth resulting in bimodal size distribution of grains in the microstructure and that results in significant variation in the hardness, (3) the grain growth is severe for the case of higher temperature (400°C) and working ratio (0.4 per direction) forging condition, and (4) the forging temperature affects the grain growth larger extent than the working ratio. The mechanisms responsible for the grain refinement and abnormal grain growth are discussed in detail.