چكيده به لاتين
Semi-solid methods are new processes in the production of materials. Inert gas injection semi-solid process (GISS) is one of these processes that have been considered recently. This method causes local and rapid heat extraction combined with the convection using the injection of Argon gas through a porous tube in temperatures above liquidus of the melt.
In this investigation, the effect of inert gas bubbling on the microstructure of AZ91 magnesium alloy at different conditions has been studied. Different parameters such as, the argon gas flow rate of 1, 2, 4 L/min, the injection temperature of 610, 620, 630℃, and the injection duration of 10, 15, 20 seconds have been investigated. It was found that the GISS process led to the microstructural modification of this alloy. Microstructural study showed that this semi-solid process changed the microstructure of AZ91 alloy from dendritic to non-dendritic and globular state.
Image analysis showed that the best sample with the highest amount of globularity (0.75), minimum average grain size (58.4µm) and minimum average grain number per square millimeter (168) was related to G-4-610-10 sample. Under these conditions, the results of mechanical tests also indicated an improvement in mechanical properties of AZ91 alloy. Based on the results of tensile tests, the GISS process increased the ultimate tensile strength (UTS) of AZ91 alloy more than 25% and yield strength (YS) more than 17%. The results of the compression test of this sample (G-4-610-10) of the AZ91 alloy also indicated an improvement of 21% in the ultimate compressive strength, 11% in compressive yield strength, and 28% in plasticity by applying GISS semi-solid process.
