Date of Award

1992

Degree Type

Thesis

Degree Name

M.A.Sc.

Department

Mechanical, Automotive, and Materials Engineering

First Advisor

Youdelis, W. V.,

Keywords

Engineering, Materials Science.

Rights

CC BY-NC-ND 4.0

Abstract

The Al-Mg-Si system is the basis of a major class of heat treatable alloys used for both wrought and cast products. Several heat treatable alloys exhibit age hardening at room temperature after a solution treatment (natural aging), and this property is exploited to develop the mechanical properties of the alloy. The active precipitate in the natural age hardening Al-Mg-Si alloys is Mg$\sb2$Si, but the precipitation is sluggish and its acceleration would be beneficial. In a previous investigation, it was shown that Be microadditions to an Al-0.75%Mg-0.50%Si alloy significantly enhances the age hardening response of the alloy, which is associated with a refinement of the Mg$\sb2$Si precipitate. A study of the precipitation kinetics showed this is due to a Be-enhanced nucleation rate. It can be shown that the nucleation rate increases with the nucleation entropy of the precipitating compound (Mg$\sb2$Si), which can be effected by the concentration of the Be in the precipitate compound, or by restricting solubilities of the precipitate's components in the Al solid solution. This study was undertaken to determine the extent to which Be can be incorporated into Mg$\sb2$Si, and its effects on the solubility of Mg and Si in Al($\alpha$). Direct spectroscopic analysis of Be using EDS is not possible due to the low atomic number of Be, and consequently the Be content must be inferred from the combined results using several techniques. In this study, the solubility determination was made using energy dispersive spectroscopy (for Al, Mg, Si), wavelength dispersive spectroscopy (for Be), X-ray diffraction, and optical microscopy coupled with microhardness. From the X-ray diffraction results, it is estimated that Be decreases the solubility of Mg$\sb2$Si in Al($\alpha$) up to about 0.3 at.% at 550$\sp\circ$C, and up to about 4.8 at.% Be may be incorporated into Mg$\sb2$Si compound. Source: Masters Abstracts International, Volume: 32-02, page: 0699. Adviser: W. V. Youdelis. Thesis (M.A.Sc.)--University of Windsor (Canada), 1992.

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