Influence of milling media on the microstructure and mechanical properties of mechanically milled and sintered aluminium

Mechanically alloyed aluminium powder was prepared by vacuum attrition milling. Two types of milling balls (steel or hard-metal balls) were employed. Powder consolidation was carried out by cold pressing and vacuum sintering. The microstructure of consolidated samples obtained from powder milled with steel balls shows needle-shaped Al-Fe intermetallics. This acicular morphology is responsible for the low elongation (1%) of these samples. However, specimens manufactured from powder milled with hard-metal balls show a different microstructure. The powder is contaminated by WC and Co, coming from the milling balls. These contaminants change the size (smaller) and the shape (spheroidal) of the intermetallics. This results in a remarkable increase in elongation (4%), without reduction in tensile strength (ca. 300 MPa).