Ageing of Liquid-Quenched and Solid-Quenched Aluminium Base Alloys; Analysis of Lattice-Parameter Variations

摘要

The thesis deals with ageing phenomena in binary aluminum alloys rapidly quenched from a high temperature to room temperature. Quenching has been performed from temperatures at which a solid (matrix) phase possesses an increased solid solubility for the solute as compared to the one at room temperature (solid quenching = SQ) and from temperatures at which the alloy investigated is in the liquid state (liquid quenching = LQ). In both cases a solute supersaturated Al matrix is obtained after quenching. Liquid quenching can provide solid alloys with special properties: (i) relatively large amounts of dissolved alloying elements and vacancies in the Al matrix and (ii) a very small grain size. The precipitation phenomena occurring on ageing after liquid quenching and after solid quenching at temperatures between 400 and 500 K have been studied. The alloys studied were AlSi and AlMg. The choice of Si and Mg as alloying elements enabled the study of two principally different precipitation mechanisms. In quenched AlSi alloys, the precipitating phase is the equilibrium (Si) phase, whereas in quenched AlMg alloys the precipitation of magnesium proceeds via a multi-stage precipitation sequence.