Powder compaction effect on foaming behavior of uni-axial pressed PM precursors

A study on foaming behaviour of metal powder precursors compacted by cold uni-axial compression is reported. PM precursors have been produced by pressing the aluminum powders in a cylindrical die, under single or double compaction. Billet densification was characterized by testing the green sample cross-sections by micro-hardness measurements. The so obtained hardness maps were correlated to the foamed sample. The results demonstrated the fundamental role played on the powder densification by wall-die frictions during the compaction operations. Best results were obtained from billets compacted by the double pressing action in a lubricated die. Finally, double compacted pellets were prepared from aluminum powders milled for different times and the pore morphology of the resulting foamed samples was evaluated in terms Of cell circularity. The powder granulometry resulted to be an other important parameter influencing the green densification and the final foam quality.