Dimensional behaviour of aluminium sintered in different atmospheres

The sinterability of pure aluminium powder was controlled in different sintering atmospheres, i.e. nitrogen, argon, nitrogen/hydrogen and nitrogen/argon gas mixtures, and also in vacuum. Dimensional changes occurring during sintering were monitored by dilatometry. Thermogravimetric analysis (TG) was used to recognize possible interactions between aluminium and nitrogen. Pure nitrogen was found to be the only active sintering atmosphere for aluminium, promoting shrinkage, associated with a weight gain by binding nitrogen, and enhancing mechanical properties of the sintered compacts. Hydrogen lowers the sinterability of aluminium very strongly, even when present in small concentrations in a nitrogen atmosphere. Auger electron spectroscopy was used to characterize the surface layers on aluminium powder particles, fractured green compacts and sintered samples. Distributions of aluminium, nitrogen, oxygen and other elements, contained as impurities, were obtained by depth profiling measurements on this surfaces. Indications are that enhanced concentration of magnesium within the powder particle surface film promotes sintering of aluminium.