Some Studies on Densification Behavior Modeling of Al-Pb Alloys Produced by Different Routes

The recent research into the alternate sliding bearing materials unequivocally point to the beneficial role of lead (Pb) in aluminum (Al). For such applications, powder metallurgical processing (P/M) of the alloys can result in homogeneous microstructure and controlled porosity. However, the cold die compaction used in P/M processing leads to inhomogeneous density distributions and non-uniform shrinkage or distortion during sintering. In order to control their final shape, the appropriate models are necessary for densification of composite powders. In the present work, the authors studied the effect of compaction pressure and BCR on densification behavior of five compositions of Al-Pb alloys processed through conventional ball milling and attrition milling routes. The premixed powder samples are subjected to compressibility test, and the changes in density are analyzed in cold die compaction. The microstructural evidence provided by the SEM photographs and the compressibility test data, together, confirms that attrition milling process and higher BCRs result in better densification in Al-Pb alloys, due to refined microstructure and improved homogeneity. Further, sigmoidal family nonlinear regression models are applied to the test data based on Levenberg-Marquardt method. Based on a two-stage validation of the best fitting mathematical models, this study establishes that Richards Model effectively predicts compact density within +/- 1% in most of the cases related to Al-Pb alloys.