Effects Of Rare Earth Elements And Heat Treatments On Microstructure And Properties Of Cu-Fe Microcomposites

The Cu-Fe filamentary microcomposites were prepared by heavy cold drawing and intermediate heat treatment. The microstructure and properties of Cu-6%Fe, Cu-12%Fe and Cu-6%Fe-RE (mass fraction) alloys were investigated at various drawing ratios and the effect of Fe content, rare-earth elements and heat treatments on the microstructure and properties of the Cu-Fe alloy was discussed.For as-cast Cu-6%Fe and Cu-12%Fe alloys, some primary Fe dendrites distribute in the Cu matrix, the original grains and dendrites of both Cu and Fe phases evolve into ribbon-like filaments during drawing deformation. The filaments align parallel to the wire axis on the longitudinal section and the Fe phase has a curled and folded morphology on the transverse section. In particular, the Fe filaments in Cu-12%Fe is more compact and finer than those in Cu-6%Fe since Cu-12%Fe has higher volume fraction of the primary Fe and more developed dendrites. For Cu-6%Fe and Cu-12%Fe alloys, the strength increases and electrical conductivity decreases with increasing in the draw ratio. Cu-12%Fe has higher strength than Cu-6%Fe due to higher proportion of Fe filaments. The main reason is line defects and face defects in crystal lattice increase with increasing in the draw ratio. Low deformation resistance and small amount of Fe phase in Cu-6%Fe result in low densities of both dislocation and interface in the deformation process. This is responsible for Cu-6%Fe with higher electrical conductivity and lower strength than Cu-12%Fe.The behavior of RE microalloying in Cu-6%Fe was investigated by observing microstructure and determining mechanical properties and electrical conductivity for the composites at various drawing ratios. Adding 0.05%～0.3% RE into Cu-6%Fe can significantly refine the dendrites of primary Fe and Cu but show an insignificant influence on the filamentary structure. The ultimate tensile strength of the composites increases but the electrical conductivity decreases with the increasing in draw ratio. RE in Cu-6%Fe can reduce the strain hardening rate and the conductivity loss rate in the range of high drawing strain. Therefore, the RE-containing alloys have lower strength and higher conductivity than the RE-free alloy at the drawing ratios higher than a certain level. The electrical conductivity increases and micro-hardness decreases with increasing annealing temperature for the three alloys. Annealed at high temperatures, the RE-containing alloys have higher electrical conductivity and hardness than the RE-free alloys. RE can enhance the softening resistance of the alloys during annealing.During aging treatment, the precipitates of Fe phase are obviously coarsen and decreased. The hardness of Cu-6%Fe alloy increases in initial aging period and then decreases. The electrical conductivity increases with the increasing of aging time. Aging treatment can significantly improve the strength and electrical conductivity of Cu-6%Fe.