楊哲人Tz- En CHANG張子恩2024-09-262024-09-262024https://ntu.primo.exlibrisgroup.com/permalink/886NTU_INST/14poklj/alma991039261578804786https://scholars.lib.ntu.edu.tw/handle/123456789/721567指導教授：楊哲人This study focuses on comparing the differences in mechanical properties and microstructure of AA7075 aluminum alloys with different copper contents after various solution heat treatments. By employing multi-stage solution heat treatments at different temperatures, the dissolution state of second phases within the aluminum alloy is observed using a Scanning Electron Microscope (SEM), differentiating it from aluminum alloys treated with traditional single temperature solution heat treatments. The process aims to optimize the time of solution treatment to achieve higher mechanical properties, and improve the poor properties of high copper content aluminum alloy. Through Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) analysis, it is found that the main second phases in AA7075 aluminum alloys are the η phase, S phase, and ω phase, with melting points of 481 °C, 493 °C, and insoluble, respectively. Different copper contents change the ratio of the second phases, especially S phases. This experiment designs solution heat treatments at 475 °C and 490 °C based on DSC results to optimize the dissolution of second phases and prevent incipient melting. The Electron Probe Micro Analyzer (EPMA) reveals that solution treatment at temperatures exceeding the melting points of second phases causes incipient melting voids, reducing mechanical properties. Single-stage solution treatment at 490°C causes the η phase to incipiently melt, leaving voids. Solution treatment at temperatures significantly below the melting points of second phases fails to dissolve them completely. The study finds that solution treatment at 475 °C leaves the S phase behind, significantly reducing mechanical properties. The study discovers that designing two-stage solution treatments for second phases, with heat treatments at 475 °C and 490 °C respectively, can solve the problems of residual phases and incipient melting mentioned-above, significantly enhancing mechanical properties. Using Electron Backscattered Diffraction (EBSD) and Transmission Electron Microscope (TEM) find no significant differences in grain size and precipitates between single-stage and two-stage solution treatments. Thus, applying two-stage solution treatment to the aluminum alloy can improve problems caused by second phases. To enhance the mechanical properties of high copper content aluminum alloys, a 500 °C third stage of solution heat treatment was introduced to eliminate the S phase remained and increase the density of precipitates. Finally, it effectively improves the strength and ductility of high copper aluminum alloys. Through analysis using TEM bright field, HRTEM, and atomic-resolution image, it was observed that, under the peak aging conditions of the three-stage solution heat treatment, the precipitates tend to be smaller compared to those in the single-stage and two-stage. Synthesizing the experimental results, it is observed that although the high-copper aluminum alloys initially exhibited inferior properties, through multi-stage solution heat treatments, the properties of high-copper aluminum alloys can achieve levels comparable to or better than those of low-copper aluminum alloys.本研究聚焦於比較不同銅含量之AA7075鋁合金經不同固溶熱處理後，機械性質與顯微結構組織之差異。探討採用不同溫度之多階段固溶熱處理，以掃描式電子顯微鏡 (Scanning Electron Microscope, SEM)觀察鋁合金內部二次相之消融狀態，與傳統單一溫度之單階固溶熱處理之鋁合金差別，並且最佳化固溶製程以達更高機械性質，並且改良高銅含量鋁合金不佳之性質。 經差示掃描量熱法 (Differential Scanning Calorimetry, DSC)及X光繞射分析儀(X-ray diffraction, XRD)分析可得，AA7075鋁合金內主要二次相為η相，S相，及ω相，熔融溫度分別為攝氏481度，493度及不固溶。並且不同銅含量鋁合金會改變內部二次相之比率，本實驗則以此溫度為依據設計475 °C與490 °C之固溶熱處理，以最佳化固溶二次相並防止二次相初熔(incipient melting)。 透過電子微探儀 (Electron Probe Micro Analyzer, EPMA)可得知，在經超過二次相熔點之溫度直接固溶會造成初熔之孔洞，並且降低機械性質。以490 °C單階固溶會造成η相初融留下孔洞。而以低於二次相熔點過多溫度固溶則無法固溶完全，透過研究結果，以475 °C固溶會使S相殘留，並大幅降低機械性質。 研究發現針對二次相進行二階段固溶設計，分別以475 °C和490 °C熱處理，可解決二次相殘留與初熔問題，並大幅提升機械性質，並且分別以背向散射繞射儀(Electron Backscattered Diffraction, EBSD)和穿透式電子顯微鏡 (Transmission Electron Microscope, TEM)觀察發現單階段與二階段固溶在晶粒大小與析出物並無明顯差異，因此對鋁合金做多階段固溶可改善二次相所造成之問題。 最後為改善高銅含量鋁合金之機械性質，新增第三階段固溶熱處理500 °C階段，以消融殘餘S相，同時增加析出物分布密度，實際可增加高銅鋁合金之強度及延伸率，透過TRM明場、HRTEM及原子級影像分析可得在經三階段固溶熱處理之頂時效條件下，析出物較前階段有變小趨勢，並且三階段固溶對高銅鋁合金之改善多於低銅鋁合金。綜合實驗結果可得，雖然原本高銅含量鋁合金性質不佳，在經多階段固溶熱處理後，高銅鋁合金性質可達不低於低銅鋁合金程度。HRTEMHAADF原子級影像AA7075 Aluminium alloyssecond phasesAA7075鋁合金solid solution treatment二次相SEM固溶熱處理incipient melting掃描式電子顯微鏡η precipitates初熔atomic-resolution imageη析出物thesis