| The intergranular corrosion(IGC)resistance of aluminum alloys is closely related to the microstructure and grain boundary characteristics.Gernerally,low ΣCSL grain boundaries has low energy than that the random grain boundaries(R),therefore the IGC resistance is higher.Increasing the proportion of low ΣCSL grain boundaries can improve the IGC resistance of aluminum alloys.In this paper,the grain precipitate phases and grain boundary character distribution(GBCD)of 7075 Al,6063Al and 2024 Al were adjusted by different heat treatment process.And GBCDs were characterized by electron backscattered diffraction(EBSD)technology.Corrosion test were carried out in 3.5% NaCl(pH=2)aqueous solution at room temperature for different times,by scanning electron microscopy(SEM)and optical microscope(OM)and the corrosion morphologies were observed.The relationship between GBCD and IGC resistance was studied,and the results were obtained as follows:For recrystallized 7075 Al,Al-Zn-Mg-Cu phase with higher Zn and Mg contentration were found on the grain boundaries,and there were Al3 Fe and Al18Mg3Cr2 at the grain boundary junctions.The GBCDs of different types of aluminum alloys were studied.The proportions of Σ1,Σ3,Σ5-29 and R boundaries in recrystallized 7075 Al were 2.44%,2.20%,10.24% and 85.12%,respectively.They were 20.05%,0.94%,7.86% and 71.14% in under-aged 6063Al;and were 19.86%,1.68%,9.19% and 69.27% in peak-aged 6063 Al,and were 19.9%,0.49%,7.73% and 71.86% in over-aged 6063 Al,respectively.This showed that the proportion of Σ1 is the highest in under-aged sample,and the peak-aged had the higest ΣCSL number of 10.87%.For 2024 Al alloys,the proportions of Σ1,Σ3,Σ5-29 and R boundaries were 15.31%,7.3%,21.07% and 56.32% in the under-aged L-LT surface;and they were 9.97%,8.1%,25.55% and 56.39% in the peak-aged L-LT surface;and were 19.38%,5.54%,13.15% and 61.94% in the over-aged L-LT surface,respectively.And on the peak-aged L-ST surface,they were 7.87%,7.02%,13.4% and 71.7%,while they were 7.08%,6.44%,10.3% and 76.18% on the ST-LT surface,respectively.This indicated that the over-aged L-LT surface had the largest number of Σ1 boundaries,while the peak-aged L-LT surface had the most ΣCSL(33.65%)of boundaries in the 2024 Al alloy.The relationship between the GBCD and IGC of different types of aluminum alloys were studied.The corroded proportions of Σ1,Σ3,Σ5-29 and R boundaryies in recrystallized 7075 Al were 66.67%,72.73%,78.57% and 91.49%,respectively.Orderly,they were 35.8%,57.1%,53.4% and 63.4% in under-aged 6063Al;and were 50.2%,64.7%,78.5% and 85.2% in the peak-aged 6063Al;and were 28.1%,33.3%,55.32% and 78.03% in the over-aged 6063 Al,respectively.For the rolled surface(L-LT)of 2024 Al,the corroded proportion of Σ1,Σ3,Σ5-29 and R boundaryies were 43.12%,50%,60.7% and 67.33% in the under-aged sample;and 21.88%,30.77%,39.02% and 40.88% in the peak-aged one;and 19.64%,0,36.84% and 48.04%,in the over-aged one,respectively.Additionally they were 18.92%,30.3%,34.92% and 51.04% in the peak-aged L-ST surface;and were 9.09%,36.67%,37.5% and 45.63% in the peak-aged ST-LT surface,respectively.The results above showed that the IGC resistance in various aluminum alloy ranked from high to low was Σ1>Σ3>Σ5-29>R boundaries. |
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