Effect of Al addition on microstructure of AZ91D

Casting is a net shape or near net shape forming process so work-hardening will not be applicable for improving properties of magnesium cast alloys. Grain refinement, solid-solution strengthening, precipitation hardening and specially designed heat treatment are the techniques used to enhance the properties of these alloys. This research focusses on grain refinement of magnesium alloy AZ91D, which is a widely used commercial cast alloy. Recently, Al-B based master alloys have shown potential in grain refining AZ91D. A comparative study of the grain refinement of AZ91D by addition of 0.02wt%B, 0.04wt%B, 0.1wt%B, 0.5wt%B and 1.0wt%B of A1-5B master alloy and equivalent amount of solute element aluminium is described in this paper. Hardness profile of AZ91D alloyed with boron and aluminium is compared

Effect of intensive melt shearing on the formation of Fe-containing intermetallics in LM24 Al-alloy

Fe is one of the inevitable and detrimental impurities in aluminium alloys that degrade the mechanical performance of castings. In the present work, intensive melt shearing has been demonstrated to modify the morphology of Fe-containing intermetallic compounds by promoting the formation of compact α-Al(Fe,Mn)Si at the expense of needle-shaped β-AlFeSi, leading to an improved mechanical properties of LM24 alloy processed by MC-HPDC process. The promotion of the formation of α -Al(Fe, Mn)Si phase is resulted from the enhanced nucleation on the well dispersed MgAl 2O 4 particles in the melt. The Fe tolerance of LM24 alloy can be effectively improved by combining Mn alloying and intensive melt shearing

Strength-ductility behaviour of Al-Si-Cu-Mg casting alloys in T6 temper

A comparative study of the mechanical properties of 20 experimental alloys has been carried out. The effect of different contents of Si, Cu, Mg, Fe and Mn, as well as solidification rate, has been assessed using a strength-ductility chart and a quality index-strength chart developed for the alloys. The charts show that the strength generally increases and the ductility decreases with an increasing content of Cu and Mg. Increased Fe (at Fe/Mn ratio 0.5) dramatically lowers the ductility and strength of low Si alloys. Increased Si content generally increases the strength and the ductility. The increase in ductility with increased Si is particularly significant when the Fe content is high. The charts are used to show that the cracking of second phase particles imposes a limit to the maximum achievable strength by limiting the ductility of strong alloys. The (Cu + Mg) content (at.%), which determines the precipitation strengthening and the volume fraction of Cu-rich and Mg-rich intermetallics, can be used to select the alloys for given strength and ductility, provided the Fe content stays below the Si-dependent critical level for the formation of pre-eutectic alpha-phase particles or beta-phase plates

The usage of computer-aided cooling curve thermal analysis to optimise eutectic refiner and modifier in Al-Si alloys

Bismuth, antimony and strontium concentrations were optimised to alter the eutectic Al-Si phase in a commercial Al-Si-Cu-Mg alloy by way of computer-aided cooling curve thermal analysis. The results show that the eutectic growth temperature shifted to lower temperatures for all three inoculants. However, addition of Sr resulted in more depression of growth temperature compared with Bi and Sb. No further significant changes were observed with increasing the concentrations to more than 1, 0.5 and 0.04 wt% of Bi, Sb and Sr, respectively. The recalescence of these concentrations, meanwhile, showed a significant increase of magnitude. A good correlation was found between the results of thermal and microstructural analysis. For Bi and Sb, the eutectic depression temperature can be used as an individual criterion to gauge optimal levels of content in the refinement of Si, whereas for Sr, both depression temperature and recalescence magnitude must be considered. Based on the observed depression in eutectic growth temperature and recalescence, it can be concluded that the optimal concentrations to refine the eutectic Al-Si phase with Bi and Sb and to modify it with Sr at the given solidification conditions were 1, 0.5 and 0.04 wt%, respectively