Influence of process control agents on microstructure and mechanical properties of Al alloy produced by mechanical alloying

The current study aims at comparing the effect of three different process control agents (PCAs)– namely methanol (ME), ethylene glycol (EG) and stearic acid (SA)– on microstructure and mechanical properties of Al–4.4Cu–0.5Mg alloy (AA) produced by mechanical alloying of elemental powders and subsequent hot extrusion. The effect of PCAs on particle size with milling time is insignificant. The average particle size of the milled powders of all samples has reached a steady state after 3 h. Even though the grain size and its distribution in all the samples in upset-forged, hot extruded, solutionised and peak aged conditions are similar, the number density and volume fraction of nanosized θ’ precipitates are observed to be higher in the case of AA–ME sample as compared to the other samples. AA–EG samples exhibited highest hardness when compared to the other samples. This can be attributed to the higher oxygen content in AA–EG sample that results in the formation of oxides that got dispersed in the matrix. Valid tensile test data was obtained only from AA–ME sample. The failure of AA–EG and AA–SA samples can be attributed to the presence of microcracks and higher oxide content. It can be concluded that nature of PCA has significant effect on oxygen pick up, size, number density and volume fraction of precipitates and in producing defect free bulk sample.