Coincidence Doppler Broadening Study of the Precipitates of a Continuous Cast AA2037 Al Alloy after Annealing and Ageing

The microstructure and precipitates of AA 2037 Al alloy before and after artificial ageing were investigated by positron lifetime and coincidence Doppler broadening (CDB) techniques. The experimental results showed that positron mean lifetime decreased slightly with increasing annealing time due to the formation of the high temperature precipitates (T phase) and recovery of defects induced by hot-rolling. CDB ratio curves observed that characteristic shape peak of Mn and Cu increased with the content of the T phase, which identified that there exist Mn and Cu elements in T phase. Furthermore, the CDB ratio curves, after artificial ageing, appeared characteristic shape peak of Mg due to the increase of low temperature precipitates containing Mg, and Mg signal was more evident when content of the T phase was lower.