چكيده به لاتين
Casting and semi-solid methods are new processes in the production of materials which by using them, due to the creation of a non-dendritic (globular) and uniform microstructure, desirable properties are obtained. One of the methods to achieve the semi-solid slurry is gas included semi-solid process (GISS).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 A357 alloy at different conditions has been studied and the optimal conditions for GISS operation has been obtained. Different parameters such as, the argon gas flow rate of 1, 2, 4 L/min, the injection temperature of 610, 615, 620, 630℃, and the injection duration of 10, 15, 20 seconds have been investigated. . Microstructural study showed that this semi-solid process changed the microstructure of A357 alloy from dendritic to non-dendritic and globular state. The optimal sample was obtained at a temperature of 610 ℃, a flow rate of 4 liters per minute and purging time of 10 seconds, and it has globularity of 70% with a fine grain structure of 47 µm grain size. To examination the mechanical properties, tension, pressure and hardness tests have been carried out, and the results show that the mechanical properties have improved compared to the as-cast sample. The hardness has decreased by about 12%, but despite that, the tensile and compressive strength has increased, so that the ultimate tensile strength for this alloy is 7% compared to the as-cast sample, the yield strength (YS) is 5%, and elongation (ℇ) is 57%.due to GISS process, The results of the pressure test in the sample (G-4-610-10) show the improvement of the ultimate compressive strength by (28%), the compressive yield strength (25%) and also the reduction of elongation (26%).Also, due to the possibility of combining the GISS process with other forming and casting methods, thixoforming of the optimal sample was performed and the mechanical properties of this sample has increased. Key words: A357 aluminium alloy, Gas induced semi solid process (GISS), Microstructure, Globular structure
