SOME ASPECTS OF WORK-HARDENING IN SINTERED ALUMINUM-IRON COMPOSITE PREFORMS DURING COLD AXIAL FORMING

Cold upsetting experiments were carried out on sintered aluminium-iron composite preforms in order to evaluate their work-hardening characte ristics. The effect of the iron content, the iron particle-size range and the initial aspect ratio of the preforms on work hardening has bee n investigated thoroughly. Analysis of the experimental data has shown that the strain-hardening exponent n increased with decreasing values of the iron powder particle-size range, also being found to be greate r for lower aspect ratio preforms compared to higher aspect ratio pref orms. Irrespective of the initial aspect ratio and the iron content, t he finer iron particle dispersoids showed an enhanced rate of work har dening, whereas a minimum level was shown by coarser iron particle-siz e dispersoids. The strength coefficient K was found to increase with d ecreasing iron particle-size range in the aluminium matrix. Both n and K values were found to decrease when the dispersed iron-particle rang e was greater (as in the present investigation). Further, it has been found that the rate of change of the n and K values were not the same for both of the aspect ratios of the preforms tested: indeed, a pronou nced difference existed. This has established that the initial geometr y of the PM preforms plays a predominant role in influencing both n an d K. In general, as the iron content in the aluminium matrix was incre ased, K was found to increase also, irrespective of the iron particle- size and the initial aspect ratio. (C) 1998 Elsevier Science S.A. All rights reserved.