Cold upsetting experiments were carried out on sintered aluminium-iron composite preforms in order to evaluate their work-hardening characteristics. The effect of the iron content, the iron particle-size range and the initial aspect ratio of the preforms on work hardening has been 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 greater for lower aspect ratio preforms compared to higher aspect ratio preforms. Irrespective of the initial aspect ratio and the iron content, the finer iron particle dispersoids showed an enhanced rate of work hardening, whereas a minimum level was shown by coarser iron particle-size dispersoids. The strength coefficient K was found to increase with decreasing iron particle-size range in the aluminium matrix. Both n and K values were found to decrease when the dispersed iron-particle range 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 pronounced difference existed. This has established that the initial geometry of the PM preforms plays a predominant role in influencing both n and K. In general, as the iron content in the aluminium matrix was increased, 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.
