On the Microstructural and Hardness Variations of the Heat Affected Zone in the AA۶۰۸۲-T۶۵۱ Weld Joints

In this paper, the variations of microstructure and hardness of the AA۶۰۸۲-T۶۵۱ welding Heat Affected Zone (HAZ) has been studied. To reach the aim, scanning and transmission electron microscopes equipped with EDS were used and hardness and micro-hardness tests were performed. The hardness of the base metal was ۱۱۲ HV, which is suitable for ۶۰۸۲ aluminum alloy in the age-hardened condition. Evaluation of hardness variations based on distance from fusion line showed that Hardness decreased throughout wide HAZ. However, the hardness of partially melted zone was higher than that of other heat affected zones due to fully dissolution of Mg۲Si precipitates and the consequent natural aging. In all specimens, there was a valley in HAZ hardness profiles with a value of about ۵۵ HV (half the base metal hardness). Microstructural investigations of this zone revealed that βʺ precipitates were transformed into β and as aresult, the zone was over aged. Moreover, the dislocation recovery caused to reduce dislocation density. Therefore, over aging and dislocation recovery was determined as HAZ softening agents. α-Al۱۵(Fe,Mn)۳Si۲ precipitates with blocky and Chinese script morphology were observed in the base metal microstructure. In the PMZ, these precipitates mainly had blocky morphology with preferential placement on elongated rolled grain boundaries. Sub-micron Mn rich spherical phases were unchanged in the HAZ relative to the base metal.

کلیدواژه ها:

۶۰۸۲-T۶۵۱ Aluminum alloy ، Welding heat affected zone ، Dislocation recovery ، Mg۲Si precipitates ، over aging