Swelling during liquid phase sintering of Al-Mg-Si-Cu alloys

Swelling during liquid phase sintering under nitrogen of Al-xMg-ySi-0.25Cu alloys from elemental powder blends (where x and y vary from 0 to 2 wt-%) has been characterised using dilatometry and differential scanning calorimetry. It is shown that swelling in these alloys occurs upon the formation of liquid phases. It is concluded that swelling is neither a consequence of unbalanced diffusion rates (the Kirkendall effect) nor the result of the specific volume expansion of the elemental powders during melting. It is suggested that swelling occurs as a result of insufficient wetting of the aluminium particles due to the presence of an oxide layer on their surface, and the subsequent separation of the particles under the influence of the surface tension.