汽車輕量化車體結構用6000系鋁合金之研究

The Study on the Weight Reduction for Body Structure of Automobile Uses 6000 Series Aluminum Alloys

沈晉輝(Chin-Hui Shen)

指導教授 ： 歐炳隆

國立中央大學/工學院/機械工程學系/博士(2007年)

摘要

本論文主要研究汽車用6000系(Al-Mg-Si)鋁合金，如何降低自然時效的負面影響，有效提升鋁合金的烤漆硬化性(烤漆後合金強度的增加值)。本論文中以板材用鋁合金6022使用於汽車車板，擠型材鋁合金6063使用於汽車車體骨架，於熱處理製程時，預時效和預應變會直接影響後續自然時效及烤漆硬化之析出擧動，所以預時效和預應變條件之擬定，微小析出粒子組織結構之建立，具有深入探討之價值，將有助於改善汽車用6000系鋁合金板材之成形性及烤漆硬化性，使汽車用6000系鋁合金板材有更大的使用空間。 本論文的主要研究方法如下，利用高分解能穿透式電子顯微鏡(HRTEM)、穿透式電子顯微鏡(TEM)、掃描式電子顯微鏡(SEM)，進行組織結構的觀察及分析;利用高靈敏度熱分析儀(DSC)、電阻量測、導電率量測，分析各析出相的析出次序、熱安定性析出時相互之間的影響;利用微小硬度機、拉伸試驗機和彎曲試驗機測量鋁合金其硬度和拉伸強度。 本論文研究第一部分主要在於低溫預時效對擠型用6063鋁合金高溫時效時析出舉動之影響，結果顯示，鋁合金經固溶．淬水處理，溫度範圍於-10~30℃長時間預時效處理時，鋁合金基地內因有GP zone (I)形成，會抑制高溫時效時β′強化相析出，致使高溫時效後強度增加量減少，此負面現象會因低溫時效溫度的提升或時間增長而更明顯。溫度範圍於40~70℃長時間預時效處理時，基地內已生成β′′相，再經高溫人工時效時並不會回溶且會繼續成長，增加材料的強度，此正面現象會因低溫預時效溫度的提升或時間增長而更明顯。 第二部分主要在研究淬水後塑性變形(預應變)對車體用6022鋁合金時效過程之影響，結果指出差排不但抑制鋁合金在自然時效期間GP Zones (I)的生成，而且提供異質的成核位置，這將會幫助它們在人工時效處理期間，提高原子的傳送使成長成為中間相β′。經預應變的鋁合金自然時效處理後，在高溫的人工時效處理初期，鋁合金硬度會直接增加，因此導入合適差排量，可以降低GP Zones (I) 回溶所引起鋁合金強度和硬度不穩定問題，也有提升時效硬化的速度，結果指出2%預應變能有效減少鋁合金自然時效30days後，對170℃人工時效30 min後強度的影響。

關鍵字

預應變 ； 自然時效 ； 析出硬化 ； 人工時效 ； 預時效 ； 6063鋁合金 ； 6022鋁合金

並列摘要

The present thesis main research has focused in particular on the heat-treatable Al-Mg-Si Aluminum alloys automobile uses 6000 series of Aluminum alloys, how to reduce the effect of this delay for natural aging (NA) on the mechanical properties of Al-Mg-Si alloys have been carried out. In addition, the hardening response to the rather short industrial paint-bake cycle is less than desired and may be further impaired by natural aging (at room temperature storage) after the solution treatment. Hence, Al-Mg-Si sheet samples were pre-strained in tension shortly after the solution treatment to improve the paint-bake response of Aluminum alloys by employing artificial aging between the solution treatment and the paint-bake cycle.
The main research approach of this thesis is as follows, the precipitation behaviors of samples of the alloy were analyzed using differential scanning calorimetry (DSC) as well as by measuring the electrical conductivity and confirmed by microstructure observation using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Tensile tests and microhardness measurements were performed to determine the mechanical properties of the samples.
This thesis studies the first part mainly to lie in the influence of low temperature pre-aging on the artificial age-hardening of a Aluminum Alloy 6063 (Al-0.72Mg-0.42Si) has been investigated in this study. The results indicate that GP zones (I) are formed in the Aluminum Alloy 6063 at 0~30℃ during a long pre-aging period. The formation of GP zones (I) will retard the precipitation of the intermediate β′ phase during artificial aging and will result in the decreasing of the strength of the alloy after the artificial aging process. Increasing either the pre-aging temperature or the holding period will significantly decrease the strength after artificial aging. The results indicate that β′′ are formed in the Aluminum Alloy 6063 at a pre-aging temperature of 40~70℃ but this has no influence on age-hardening after artificial aging, even for a long period. Increasing either the pre-aging temperature or the holding period will significantly increase the strength after artificial aging. However, for pre-aging at -10℃, the negative effect on age-hardening is still not clear and should be investigated in the future.
The second part mainly in the study of the effect of pre-straining on the natural aging and artificial aging of an Aluminum Alloy 6022 (Al-0.6Mg-1.0Si) has been investigated in this study. The results indicate that the dislocations would not only suppress clustering during natural aging but also provide heterogeneous nucleation sites. There are particularly noteworthy results, that 2% pre-straining leads to a significant reduction in the detrimental effects of 30 days of natural aging on the artificial aging at 170℃ for 30 min and provide sufficient formability to make the part, and a high strength after the artificial aging.

並列關鍵字

Pre-straining ； Pre-aging ； AA6022 ； Natural ag ； AA6063

參考文獻

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