Abstract
An attempt has been made to optimize the solutionizing temperature and duration by observing microstructural changes along with physical and mechanical properties of a hypoeutectic Al–Si (BS LM16) alloy. The specimens were solutionized over a range of temperatures (763, 778, 793, 813 and 833 K) and duration.
Solutionizing at 763, 778 and 793 K revealed significant morphological changes in the microconstituents while the specimens at 813 and 833 K suffered from partial melting. The former group of temperatures offered significant improvement in physical and mechanical properties of the alloy while the latter one caused deterioration in properties. Coarsening of phases was found to cause a reduction in hardness, density, strength and ductility of the alloy beyond certain solutionizing duration at 763, 778 and 793 K.
The resolidified regions, where partial melting had occurred as a result of solutionizing at 813 and 833 K, possessed significantly higher hardness resulting from their refined microstructure as compared to the unaffected part of the specimens. Inspite of this, the specimens suffered from deterioration in their overall hardness due to the formation of secondary porosity and microcracking. Reduced density, strength and ductility and increased electrical resistivity of the alloy also agreed well with the generation of porosity and microcracks at these temperatures. The positive influence of increased hardness and refined microstructure of the resolidified regions seemed to have been outweighed by the predominant ill-effects of the porosity and microcracking as observed by the deterioration in the properties of the alloy at 813 and 833 K.
The study indicated that solutionizing the alloy in the temperature range of 778–793 K for 2–8 h offers spheroidized constituents and improved properties which can exhibit good results during its ageing.
