Study on refinement of recrystallized grain size of 3S alloy

Abstract

Precipitation behavior of the precipitates formed during the preheating of Al-Mn(-1.9%), Al-Mn(1.1%)-Fe(-1%), Al-Mn(1.1%)-Si(-0.6%) and Al-Mn(1.1%)-Fe(-1%)-Si(-0.7%) alloys has been investigated by means of measurements of the electrical resistance and micro-hardness, X-ray analysis and microscopical examination.Results obtained are as follows:(1) The precipitates in Al-Mn and Al-Mn-Fe alloys are MnAl6 accompained by G phase (MnAl12), and in the Al-Mn-Si alloy, are α (MnSi) at the first stage and MnAl6 at the second stage. MnAl6 is needle-like and has a property of coarsening the grain by heating, but α (MnSi) is of much finer particles than MnAl6 and has no tendency of grain growth.(2) Addition of Si in the Al-Mn alloy acceralates the velocity of precipitation which takes place more quickly than in the case of Fe in the alloy.(3) The recrystallized grain in the Al-Mn and Al-Mn-Fe alloys becomes finer after heating, but in the Al-Mn-Si alloy, the recrystallized grain is coarser after heating.This peculiar phenomenon may be explained as follows: Al-Mn-Si alloy has an uniform distribution of a great number of fine precipitates which results in an uniform distribution of working strain followed by a slow nucleation rate. The precipitates in the Al-Mn and Al-Mn-Fe alloys, however, are of large grains and have an irregular distribution of particles which result in a non-uniformity of strain distribution followed by a high nucleation rate.