氮?dú)庵腥蹮扐Z91D鎂合金
(清華大學(xué) 機(jī)械工程系 先進(jìn)成形制造重點(diǎn)實(shí)驗(yàn)室， 北京 100084)
摘 要: 在一次性充入含0.01%HFC134a(體積分?jǐn)?shù))的氮?dú)獾拿芊馊蹮挔t中， 研究了表面攪拌、 熔煉溫度和熔煉爐密封質(zhì)量對(duì)AZ91D鎂合金保護(hù)效果的影響以及氣氛對(duì)熔煉坩堝內(nèi)壁的腐蝕， 并對(duì)表面膜形貌、 厚度和成分進(jìn)行了研究。 研究結(jié)果表明， HFC134a適合充當(dāng)鎂合金在密封熔煉爐中保護(hù)氣體， 氮?dú)馐且环N好的載氣。 無(wú)表面攪拌時(shí)， AZ91D鎂合金的最高保護(hù)溫度是865 ℃； 有表面攪拌時(shí)， 最高保護(hù)溫度是800 ℃。 允許熔煉爐內(nèi)壓升率超過10 kPa/min。 所有保護(hù)膜呈致密胞團(tuán)狀結(jié)構(gòu)， 膜厚度在1~2 μm之間， 且比較均勻。 而AZ91D鎂合金不被保護(hù)時(shí)， 表面膜呈絮狀， 膜厚度在2~5 μm之間變化， 厚度很不均勻。 隨熔煉溫度升高， 表面膜中C含量逐漸減少到零, 表面膜中氧含量逐漸升高。 爐內(nèi)氣氛對(duì)熔煉爐內(nèi)壁無(wú)可觀察到的腐蝕。
關(guān)鍵字: 鎂合金; 密封爐; 保護(hù)氣體; 表面膜
（Key Laboratory for Advanced Manufacturing by Materials Processing Technology, Department of Mechanical Engineering, Tsinghua University,
Beijing 100084, China）
Abstract: The effects of holding temperature， stirring and furnace seal quality on the protection of AZ91D magnesium alloy were investigated in a sealed furnace filled once with N2 containing 0.01%HFC134a (volume fraction) before the experiments， the corrosion of the atmosphere to the inner wall of the furnace was analyzed. The morphology, thickness, and composition of the surface films were also studied. The results show that HFC134a is suitable to be the protective gas of magnesium alloys and N2 is a good carrier gas for HFC134a. Without surface agitation, the highest protective temperature for AZ91D melt is 865 ℃; with surface agitation, the highest protective temperature is 800 ℃, and the allowable pressure rising velocity in crucible can exceed 10 kPa/min.The morphology of all protective surface films reveals a compact cellular structure with an evenly distributed thickness of 1-2 μm, whereas that of unprotective films reveals a wadding like structure with an uneven thickness. With the increase of the holding temperature, the carbon content in surface films decreases to zero, and the oxygen content increases gradually. No corrosion of the atmospheres to the inner wall of the furnace is found during the experiments.
Key words: magnesium alloy; sealed furnace; protective gas; surface film
