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在钢铁和高温合金上渗铝,可以大大提高这些材料抗高温氧化和热腐蚀的能力。目前工业上常用的渗铝方法有固体包装法和热浸法。固体包装法是将工件埋在含有铝铁合金粉和氧化铝粉的混合物中,加热到850°至1000℃,保温5至24小时而获得渗铝层。此法不需特殊技术,但要先制备铝铁合金,而装箱、进炉出炉,卸出工件劳动较多,因为连箱加热,渗铝速度慢,因之所需时间很长,为其缺点。热浸法是将工件浸于熔融铝浴中而获得渗铝层,速度较快且操作简便,但铁在铝液中有一定程度的腐蚀溶解,工件渗铝后表面常不均匀,有铝堆集,而且由于金属铝的蒸发和氧化,铝的损耗也较大,此外渗铝层脆性较大.需要进行渗后热处理,这些都是热浸法不足之处。熔盐电解法渗铝是在坩埚(石墨或金属)中盛金属铝(可用铝屑),上面放1:1(分子比)的NaCl+KCl混合盐,另加少量冰晶石。坩埚和铝接为阳极,工件接为阴极。在惰性气氛保护下加热使盐熔化,然后通电流,铝作为阳极被熔盐腐蚀而生成铝离子,在阴极(工件)上沉积。由于工件不在铝浴中,故不被铝溶解,且受到阴极电流的保护作用,故不被熔盐腐蚀。铝上有熔盐复盖,蒸发和氧化均较小,故铝的损耗亦小。渗铝层较均匀,渗后不必另行热处理.沉积的铝量主要决定于电流密度与时间,服从法拉第定律,与温度无关.电流效率约在82约91％间,平均约85％。沉积的铝在高温下与底金属相互扩散而形成渗铝层,其厚度决定于温度、时间及电流密度。用电子探针分析、X-射线衔射分析及金相检查,得知纯铁上电解渗铝层最外表面有一薄层金属铝,往内为Al_3Fe、Al_5Fe_2、AlFe及AlFe_3。钢铁经熔盐电解渗铝后,抗高温氧化性能大为提高。高温合金用此法渗铝后,抗热腐蚀性能亦显著改进。
Aluminizing steel and superalloy greatly enhances the ability of these materials to withstand high temperature oxidation and hot corrosion. Currently used in industrial aluminizing methods are solid packaging and hot-dip method. Solid packaging method is the workpiece buried in a mixture containing aluminum and iron alloy powder and alumina powder, heated to 850 ° to 1000 ℃, holding 5 to 24 hours to obtain aluminized layer. This method does not require special technology, but first prepared ferroalloy, and packing, into the furnace, unloading work more labor, because even the box heating, aluminizing speed is slow, which takes a long time for its shortcomings . Hot-dip method is the workpiece immersed in the molten aluminum bath to obtain aluminized layer, faster and easy to operate, but the iron in the molten aluminum has a certain degree of corrosion and dissolution, the workpiece surface aluminized often uneven, with aluminum heap , But also due to the evaporation and oxidation of aluminum metal, aluminum loss is larger, in addition aluminous layer brittle more need to post-seepage heat treatment, these are hot-dip inadequacies. Molten salt electrolysis aluminizing is in the crucible (graphite or metal) Sheng metal aluminum (available aluminum scrap), put 1: 1 (molecular ratio) NaCl + KCl mixed salt, plus a small amount of cryolite. Crucible and aluminum connected to the anode, the workpiece connected to the cathode. The salt is melted by heating under inert atmosphere and then energized. Aluminum is corroded by molten salt as an anode to form aluminum ions and deposit on the cathode (workpiece). As the workpiece is not in the aluminum bath, it is not dissolved by aluminum, and by the cathodic current protection, it is not molten salt corrosion. Aluminum has a molten salt cover, evaporation and oxidation are smaller, so the loss of aluminum is also small. The aluminized layer is more uniform and does not require additional heat treatment after infiltration.The amount of aluminum deposited is mainly determined by the current density and time, subject to Faraday’s law and independent of temperature, and the current efficiency is between about 82% and about 85%. The deposited aluminum interpenetrates with the base metal at elevated temperatures to form an aluminized layer, the thickness of which depends on temperature, time and current density. Electron probe analysis, X-ray diffraction analysis and metallographic examination showed that there was a thin layer of aluminum on the outermost surface of the pure aluminum electrowetting aluminized layer, with Al 3 Fe, Al 5 Fe 2, AlFe and AlFe 3 3 inward. After the molten iron electrolysis aluminized steel, high temperature oxidation resistance greatly improved. After the high-temperature alloy aluminizing with this method, the hot corrosion resistance is also significantly improved.