- 學位論文
預時效和自然時效對6066與6082鋁合金人工時效硬化行為之影響
The Influence of Pre-aging and Natural Aging on the Artificial Aging Hardening Behavior of 6066 and 6082 Aluminum Alloys
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摘要
6000系列鋁合金為可析出強化型鋁合金，其主要溶質為鎂與矽，利用時效過程中析出的奈米級Mg2Si序列硬化相使鋁合金強度上升，所以鎂、矽比例與總量會大幅的影響其析出硬化行為，除此之外， 6000系列鋁合金具有遠高於鋼鐵之比強度、抗腐蝕、可鍛、可焊以及表面處理之特性，所以廣泛的應用在建築與交通工具上。在車輛板金應用中，為了使鋁合金強度上升，工廠會實施固溶、淬火與析出強化熱處理，而在固溶熱處理且淬火後之存放與運輸，即，自然時效之導入，將會在烤漆工序時之烘烤硬化產生自然時效之負面效應，造成鋁合金強度不如預期。 本實驗將利用多種熱處理，從而驗證6066與6082鋁合金之自然時效負面效應，接著導入各式預時效參數，分析其減緩負面效應之效力，並且從各種熱處理參數中，比較6066與6082鋁合金在析出行為與機械性質上之差異。 在第一部分中，本實驗將比較6066與6082鋁合金在自然時效與人工時效下析出行為與機械性質之差異，由實驗結果得知，6066鋁合金因具有較高的鎂、矽總量與銅含量，使其在自然時效過程中生成大量細小的團簇，造成硬化速率與T4狀態下的穩定硬度明顯高於6082鋁合金，而在人工時效的部分，銅的加入會細化析出物與加速析出動力學並且會生成熱穩定極高之鋁鎂矽銅(QP2)硬化相，造成6066鋁合金在較短的時間內可以達到尖峰時效並且具有比6082鋁合金更高的尖峰硬度與過時效之熱穩定性。 在第二部分中，本實驗實施NA+PB (175℃ x 30min)與NA + 175℃尖峰時效之熱處理用以驗證自然時效對烘烤硬化後的負面效應以及了解自然時效對尖峰時效後的影響，其中6066 鋁合金因在自然時效過程中生成較多的團簇以及在無自然時效下(NA 0hr + PB狀態)較快的析出速率使烘烤硬化後的硬度縮減率明顯高於6082鋁合金，除此之外，在T4 + 175℃尖峰時效之熱處理條件中，低鎂矽比鋁合金因長時間人工時效過程中，富鎂團簇因熱穩定性較低會溶回基地補充析出所需要的溶質，而富矽團簇不會持續成長消耗溶質且基地內還具有足夠之矽原子，使人工時效中期的過程中，主要強化相β"的析出並不會受到明顯抑制，造成尖峰時效後硬度並沒有因自然時效而有明顯的下降。 在第三部分中，本實驗為了解決第二部分因自然時效對烤烘烤硬化後之負面效應，所以在自然時效前導入預時效熱處理來減緩負面效應之影響，研究結果發現6066與6082鋁合金經過120℃ x 1hr之預時效處理後，有最佳抑制自然時效負面效應之能力，6066鋁合金在120℃ x 1hr預時效加入前(NA+PB)因自然時效造成之硬度縮減率為14.8%，而在加入預時效後則降至1.4%；6082鋁合金在預時效加入前的硬度縮減率為9.6%，加入預時效後則降為3.7%，此結果與6066鋁合金具有較快的析出動力學與鎂矽總量有關，造成預時效過程中大量細小且分散的GP-zone生成，間接減緩了後續自然時效時團簇的形成，所以在烤漆熱處理後，受自然時效造成之硬度縮減率大幅下降。
並列摘要
The 6000 series aluminum alloys are precipitation-hardenable alloys that are primarily composed of magnesium and silicon. During the aging process, nano-sized Mg₂Si precipitates form, enhancing the alloy's strength. Consequently, the proportion and total amount of magnesium and silicon exert a significant influence on the precipitation hardening behavior. Furthermore, the 6000 series aluminum alloys exhibit superior specific strength compared to steel, in addition to corrosion resistance, forgeability, weldability, and surface treatment capabilities. As a result, they are widely utilized in the construction and transportation industries. In the automotive industry, factories employ solution treatment, quenching, and precipitation hardening heat treatment to enhance the strength of aluminum alloys. Nevertheless, the introduction of natural aging during storage and transportation after solution treatment and quenching can negatively impact the strength of paint-baking hardening, resulting in a lower-than-anticipated strength. The objective of this experiment is to verify the negative effects of natural aging on 6066 and 6082 aluminum alloys through the utilization of various heat treatments. Subsequently, different pre-aging parameters will be introduced to analyze their effectiveness in mitigating these negative effects. The differences in precipitation behavior and mechanical properties of 6066 and 6082 aluminum alloys under various heat treatment parameters will also be compared. In the first part of this experiment, the differences in precipitation behavior and mechanical properties of 6066 and 6082 aluminum alloys under natural aging and artificial aging will be compared. Experimental results show that due to the higher total amount of magnesium and silicon and the copper content in 6066 aluminum alloy, a large number of fine clusters form during the natural aging process. This results in a significantly higher hardening rate and stable hardness in the T4 state compared to 6082 aluminum alloy. In the case of artificial aging, the addition of copper refines the precipitates and accelerates the precipitation kinetics, forming the highly thermally stable Al-Mg-Si-Cu (QP2) hardening phase. Consequently, 6066 aluminum alloy can reach peak aging in a shorter time and has a higher peak hardness and thermal stability in the over-aged condition than 6082 aluminum alloy. In the second part of this experiment, NA+PB (175℃ for 30 minutes) and NA + 175℃ peak aging heat treatments were conducted to verify the negative effect of natural aging on bake hardening and to understand the influence of natural aging on post-peak aging. For 6066 aluminum alloy, due to the formation of more clusters during the natural aging process and a faster precipitation rate in the NA 0hr + PB state (without natural ag-ing), the reduction in hardness after bake hardening is significantly higher than that of 6082 aluminum alloy. Additionally, under the heat treatment condition of T4 + 175℃ peak aging, low Mg/Si ratio aluminum alloys exhibit dissolution of Mg-rich clusters back into the matrix to supply the solutes needed for precipitation during long-term artificial aging due to their lower thermal stability. In contrast, Si-rich clusters do not continue to grow and consume solutes, and there are still enough silicon atoms in the matrix. Therefore, during the intermediate stage of artificial aging, the precipitation of the main strengthening phase β'' is not significantly suppressed, resulting in no obvious decrease in hardness after peak aging due to natural aging. In the third part of this experiment, to address the negative effects of natural aging on bake hardening mentioned in the second part, pre-aging heat treatment was introduced before natural aging to mitigate these negative effects. The study found that 6066 and 6082 aluminum alloys, after pre-aging treatment at 120℃ for 1 hour, had the best ability to inhibit the negative effects of natural aging. For 6066 aluminum alloy, the hardness re-duction rate due to natural aging before the introduction of pre-aging (NA+PB) was 14.8%, which decreased to 1.4% after pre-aging. For 6082 aluminum alloy, the hardness reduction rate before pre-aging was 9.6%, and it decreased to 3.7% after pre-aging. This result is related to the faster precipitation kinetics and the total amount of magnesium and silicon in 6066 aluminum alloy, causing the formation of a large number of fine and dispersed GP-zones during the pre-aging process, indirectly mitigating the formation of clusters during subsequent natural aging. Therefore, after the baking heat treatment, the hardness reduction rate caused by natural aging significantly decreased.
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