| 摘要: | 本研究係探討固溶處理前之冷加工量(0%、5%、10%、20%、30%、50%)以及不同時效處理(T6、T76、T77)對於AA7055高強度鍛造鋁合金微結構與機械性質的影響，藉由光學顯微鏡(OM)、穿透式電子顯微鏡(TEM)、導電度量測(%IACS)、拉伸試驗以及維氏硬度計等，研究合金加工量對微結構與機械性質的影響。
結果顯示，當冷加工量越大時，產生的輥軋織狀晶就越多，並且在30%以上的冷加工量產生一組平行的剪切帶，在50%的冷加工量時，出現第二組，並且剪切帶與加工方向的角度逐漸減小。熱處理(T76)後，加工過的合金發生退火的三個階段，分別是回復、再結晶以及晶粒成長，而再結晶的程度是隨著加工量的增加而增加，而晶粒成長後的晶粒尺寸則與加工量成反比。冷輥時，硬度逐漸上升、導電度逐漸下降，固溶處理後，硬度及導電度回復至未冷加工的狀態。另外，合金經過T6時效處理後晶界上擁有細密連續的析出物，經提高時效溫度的T76與T77時效，晶界上析出物呈現粗大且不連續狀，也有無析出帶(Precipitation free zone, PFZ)的產生；由於基地與析出物之電位差，不連續狀之析出物使得T76與T77擁有較佳的抗剝落腐蝕能力。T76態因時效時間的延長也使得晶粒內之析出物粗大而降低合金之強度，T77態因重新再時效而有效地將強度回到頂時效之強度。
關鍵字: AA7055、冷輥、織構、再結晶
;This study investigated the effects of cold working before solution treatment (0%, 5%, 10%, 20%, 30%, 50%) on the microstructure and mechanical properties of AA7055-T76 high strength forged aluminum alloy, and improved AA7055-T76 High-strength aluminum alloy properties, by optical microscope (OM), conductivity measurement (% IACS), tensile test and Vickers hardness tester, etc. , to study the effect of alloy processing on microstructure and mechanical properties .
The results show that when the amount of cold working is larger, the number of texture structure increase, and the cold working amount of more than 30% produces a set of parallel shear bands, and at the 50% cold working amount, the second group appears. Also, the angle of the shear band to the rolling direction is gradually reduced. After heat treatment (T76), the processed alloy undergoes three stages of annealing, namely recovery, recrystallization & growth, and the degree of recrystallization increases as the amount of processing increases. The grain size after grain growth is inversely proportional to the amount of processing. In the case of a cold roll, the hardness gradually rises and the conductivity gradually decreases. After the solution treatment, the hardness and electrical conductivity recover to the state of not being cold worked. In addition, AA7055 aluminum alloy has fine and continuous precipitates on the grain boundary after T6 aging treatment, and the aging temperature is increased by T76 and T77. Thus, the precipitates on the grain boundary are coarse and discontinuous, and the precipitate free zone(PFZ) occur; due to the potential difference between the substrate and the precipitates, the discontinuous precipitates make T76 and T77 have better resistance to exfoliation corrosion(EXCO). The elongation of the T76 state also causes the precipitates in the grains to be coarse and the strength of the alloy to be lowered. The T77 state effectively returns the
strength to the peak aging due to re-aging.
Keywords: AA7055, cold roll, texture, recrystallization |
