| 摘要: | 本研究藉由顯微結構觀察、差示掃描量熱法、機械性質與腐蝕性質(剝落腐蝕、極化腐蝕與耐應力腐蝕性)試驗等，探討Cu (1.2, 1.9 wt%)與三段式加強型固溶處理(EST, enhanced solution treatment)對AA7056（Al-9.0Zn-2.3Mg-xCu-0.05Zr）高強度鍛造型鋁合金機械性質與腐蝕性質的影響。結果顯示，合金機械強度隨Cu含量的提升而有顯著增加，然而合金在均質化後的殘留S-Al2CuMg相也將隨之增加，導致合金腐蝕電位下降，因而損害合金之抗腐蝕性質；而含低Cu之合金，雖因析出強化相η’-MgZn2相(與η-MgZn2相)析出量減少而減損了合金強度，但卻能有效減少殘留S-Al2CuMg相，因而提升了合金抗腐蝕性。
另外，相較於一段式固溶處理，當合金施以三段式加強型固溶處理，除了能提升合金之析出動力，增加強化相η’-MgZn2相(與η-MgZn2相)析出量，而強化合金外，還能顯著減少S-Al2CuMg相之數量，且晶界上η-MgZn2平衡相的Cu濃度也大幅提高，進一步提升合金晶界周圍的腐蝕電位，使得合金獲得較佳的耐腐蝕性。
綜上結果發現，含高Cu (1.9 wt%)的Al-9Zn-2.3Mg-xCu-0.05Zr合金當施以三段式加強型固溶處理，能獲得最佳機械強度與良好抗腐蝕性。且能在不發生過熱的同時，增加合金固溶溫度與加工溫度，將有助於合金熱加工速率之提升。
;This study used microstructure observation, differential scanning calorimetry, corrosion properties and mechanical property (exfoliation corrosion, polarization corrosion, and stress corrosion resistance) tests, etc., to discuss the effects of Cu content (1.2, 1.9 wt%) and enhanced solution treatment (EST) on mechanical properties and corrosion resistance of Al-9.0Zn-2.3Mg-xCu-0.05Zr high-strength forging aluminum alloy. The results showed that the strength of the alloy increased significantly with the increasing of Cu content, which led to a decrease in the corrosion potential of the alloy, thus impairing the corrosion resistance of the alloy. However, the alloy with low Cu content reduced the strength of the alloy due to the decrease in the precipitation of the η′-MgZn2 phase (and η-MgZn2 phase), but it could effectively reduce the residual S-Al2CuMg phase. Therefore, the alloy′s corrosion resistance was improved.
In addition, compared with the single-stage solution treatment (SST), the alloy subjected to the enhanced solution treatment (EST) could not only increase the precipitation power and the precipitation of η′-MgZn2 phase (and η-MgZn2 phase) to strengthen the alloy, but also significantly reduce the S-Al2CuMg phase. The Cu concentration of the η-MgZn2 phase on the boundary was also greatly increased, which further increased the corrosion potential around the alloy grain boundary, so that the alloy had better stress corrosion resistance.
Based on the above experimental results, it was found that Al-9Zn-2.3Mg-xCu-0.05Zr alloy with high Cu content (1.9 wt%) treated with the enhanced solution treatment could obtain the best mechanical properties and good corrosion resistance. Moreover, the solid solution temperature and hot working temperature of the alloy could also increase without overheating, which would help to increase the alloy hot working rate. |
