Synthesis Optimization Of Microstructure And Mechanical Property In Aluminium Casting Alloy With Obdurability

The Al-Si casting alloys's mechanical properties are strongly influenced by grain size, distribution and morphology of α-Al dendritic crystal and eutectic-silicon, heat treatment. Accordingly, melt treatment and heat treatment for the alloys are made to improve solidification morphologies and increase mechanical properties. This thesis regarded A357 alloy as the research object. The effects of refinement and modification on the microstructure of alloys have been investigated by adding the refiner and modifier in the melt, the sensibility to wall thickness in A357 alloy was also studied. The research aspects of the paper are as follows:1. The Sr-modified structures exhibited fibrous Si and Sr-modified alloys are significantly higher than those of the Na-modified and the Sb-modified alloy in tensile properties and yield strength. Eutectic Si particles of Sr-modified alloys are palletized obviously, thinner and rounder than the Na-modified. Eutectic Si phases are staggered pattern with α-dendrites on crystal boundary in modified better alloy. The phase interfaces hindrance gliding and make it difficult to deform for alloy, and so the more eutectic structures, the higher intensity and the lower plasticity . Sb is weaker more than Na in modifying ability, and microstructure of eutectic-Si may be changed from flakes to fibrous by Sb modified. The Sb-modified alloy's elongation was highest in the three modifiers.2.The results show that Al-5Ti-B not only inhibit primary dendritethe growed and hence refined primary dendrite, but also Si particles were obviously refined as the grains were refined in A357 alloy, and the shape of Si was improved. The effects of titanium content on the yield strength and tensile strength of alloys were trifling, but the effects on the ductility were obvious which increased primarily and then decreased with increasing titanium content.3. Effects of both Al-5Ti-B refiner and Na modifier on the microstructure and mechanical properties of A357 alloy during die-casting were experimentally studied. The results showed that the optimal addition of Al-5Ti-B refiner and Na modifier was respectively 0.15% and 1.5%. The mechanical properties were higher than Na modifier alone, however, lower than Al-5Ti-B refiner alone, when the optimal contents of Ti and Na additions were combined in the melt.