Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/9487
標題: 外在塗覆鎵元素對AA6061Al-Mg-Si合金沿晶破斷、晶界鎂元素增加及拉伸性質弱化之研究
Gallium-induced intergranular embrittlement, magnesium enrichment on grain boundary and the degradation of tensile properties of AA6061 Al-Mg-Si alloy after gallium treatment
作者: 張呈嘉
Chang, Cheng-Chia
關鍵字: Ai-Mg-Si alloy;鋁-鎂-矽合金;gallium;intergranular fracture;Auger electron spectroscopy;tensile properties;鎵;沿晶破斷;歐傑電子能譜儀;拉伸性質
出版社: 材料科學與工程學系
摘要: 
本研究之目的在探究鎵效應對鋁合金液態金屬脆化的影響,首先是要發展出一種令人滿意的新破斷處理方式,在室溫下就能使AA6061鋁合金產生沿晶破斷。再者,透過改變塗鎵量、放置溫度及試片取樣方向,釐清各種變數對鋁合金脆化程度的關係。研究的另一個重點為不同系列的鋁合金(AA6061及AA1050鋁合金)進行晶界元素分析的研究,由於兩合金的最大差異處為鎂含量的含量不同,藉此可了解液態鎵是否會導致鋁合金晶界的鎂、矽元素提高,而造成更嚴重的脆化。
根據SEM破斷面觀察,未經過鎵處理試片的破斷模式呈現延性破斷;而經過鎵處理試片的破壞模式大多為沿晶破斷;若將塗鎵量控制在一個臨界值,則鋁合金破壞模式仍保持為沿性破斷,由此證實了不同的塗鎵量將會使得鋁合金的破斷模式有所不同。而拉伸試驗結果顯示經過鎵處理試片的拉伸荷重皆有所下降,塗鎵量的多寡對鋁合金拉伸性質的影響程度也有所不同,拉伸荷重會隨著塗鎵量增加而明顯降低。針對試片破斷面作AES晶界元素檢測,得知不同試片取樣方向的試片,會有不同的鎂晶界含量。試片長軸垂直於軋延方向的試片之鎂晶界含量顯著高於試片長軸平行於軋延方向的試片,並且晶界鎂含量是隨著塗鎵量的增加而提高。由歐傑電子分析儀(AES)的表面元素分析結果得知在晶界的鎂增加現象並不會因為沿晶破斷面的氧化而造成。再者,由不同型號鋁合金的脆化實驗得知AA6061鋁合金經過鎵處理後所導致脆化的原因有兩種,第一是液態鎵的影響,第二是鎵會導致鎂集中於試片之晶界及自由表面,使晶界強度的降低,並且造成更進一步的晶界脆化;然而,AA1050鋁合金的脆性破壞僅受到液態鎵鎵的影響。在相同塗鎵量的AA1050鋁合金的拉伸荷重明顯高於AA6061試片,並且破斷模式是由沿晶及延性混合型破斷所組成,代表此合金雖然受到鎵的影響,但是仍維持一定的延性。
經由本研究探究鎵效應對鋁合金液態金屬脆化的影響,成功發展出一套沿晶破斷的新處理方式;並且證實了塗鎵量、放置溫度及試片取樣方向都會影響液態金屬脆化行為,釐清了各項變數之間的相對關係。

Abstract
The purpose of this dissertation was undertaken to investigate the effect of gallium on the liquid metal embrittlement of aluminum alloy. This work was conducted to develop a pragmatic and satisfactory procedure to promote intergranular cracking for ductile AA6061 Al-Mg-Si alloy at room temperature. The study was also consider the various amount of Ga, holding temperatures and the sample with various rolling directions on the severity of liquid metal embrittlement, respectively. In addition, there remain uncertainties as to the magnitude of the grain boundary chemical composition of AA6061 samples induced by the embrittling agents and its effects on intergranular fracture. To answer these questions, AA1050 sample was used for comparison to determine whether alloying elements would correlate with Ga-induced embrittlement that governed the occurred of intergranular fracture in the AA6061 sample.
According to the SEM observation, the ductile fracture from the samples without any Ga applied on them was observed. The almost fracture surface of samples with Ga was found to be predominantly intergranular. However, intergranular fracture of samples did not occur when the amount of Ga in contact with the sample was less than a critical value. The results proved that the amount of Ga clearly affected the degree of embrittlement of aluminum alloy. The tensile test results showed that the tensile load of Ga-treated sample was significantly higher than that of the samples without any Ga applied on them. When the Ga applied to the samples, the tensile properties of these samples markedly deteriorated. The tensile load and the ratio of dimpled area for the AA6061 sample declines as the amount of Ga applied on them increases. The AES peak-to-peak ratio IMg/IAl showed that the magnesium enrichment on grain boundary is associated with the rolling direction of the sample. Mg enrichment on grain boundaey boundary in the sample whose longitudinal axis was parallel to the rolling direction is relatively weak. A high peak intensity of Mg was observed in the sample whose longitudinal axis is perpendicular to the rolling direction. The AES results also showed that the enrichment of Mg on the grain boundary does not follow from oxidation of the intergranular fracture surface, even though Mg has a high affinity for O. The AES depth profiles indicated that Ga affected the depth profiles of Mg, Al, and O from the surface to the interior. The Mg profile showed a decreasing tendency from the surface to the interior of the sample. In contrast to the Mg profile, the concentration of Ga had a rapid increase from the surface to interior. The reason of embrittlement of Ga-treated AA6061 and AA1050 samples was compared with that of AA1050 sample. The embrittlement of the AA6061 samples with Ga involves a combination of the following two effects: Ga metal on grain boundary embrittlement, and Ga-induced Mg enrichment on grain boundary that further decreases the strength of the grain boundary. However, the behavior of embrittlement of AA1050 sample was occurred due to one of Ga on grain boundary.
In this dissertation examines the effect of Ga on liquid metal embrittlement of aluminum alloys. It provides a new method for fracturing the sample intergranular at room temperature. Moreover, this dissertation was also explained that the amount of Ga, holding temperature and the samples with various rolling directions on the severity of liquid metal embrittlement.
URI: http://hdl.handle.net/11455/9487
Appears in Collections:材料科學與工程學系

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