Influence of homogenization treatment in an electric field on the workability of 1420 Al-Li alloy during hot rolling

Abstract

In A1-Li alloys after casting, a significant amount of dendritic segregation is present, which leads to collapse during bot rolling. Antes [1] shows that a dramatic improvement in ductility is achieved by eliminating dendritic segregation. The effect of undissolved second phase on ductility has been investigated by Singh and Flemings [2]. Their results show that the ductility during hot rolling depends on not only the volume fraction but also the shape and the distribution of second phase particles. For a given amount of second phase, spherical shape and random distribution of second phase particles are beneficial for the improvement of ductility. Purdy and Kirkaldy [3] have drawn attention to the advantages to be gained by homogenization at temperamre above the melting point of segregated alloys. However, for A1-Li alloys, high temperature homogenization treatment results in local overheating or local underheating and a heavy loss of Li. The homogenization process invented by David [4] is to heat slowly at rates not exceeding 50°C/h to temperature of at least 530°C up to a final homogenization. But, due to the difficulties in controlling temperature, the total content of Li and Mg is not permitted to exceed 6%. Deformation of segregated alloys promotes the homogenization of alloys [5]. However, for the as-cast A1-Li alloys, great risk of collapse exists during deformation. The heat treatment of 2091 AI-Li alloy with an electric field has been investigated [6, 7]. The results show a significant effect of the electric field on the diffusion and phase transformation of 2091 A1-Li alloy. In this letter, the effect of an electric field on the workability of 1420 A1-Li alloy is reported. 1420 A1-Li alloys were melted under an argon atmosphere. Table I gives the chemical compositions of the alloy. Ingots were treated either with or without an electric field at the same homogenization time (32 h) and temperature (470 °C). The effect of homogenization time (16 h, 24 h, 32 h) in an electric field on the volume fraction, shape and distribution of second-