【作者】 张震；

【导师】 刘会杰；

【作者基本信息】 哈尔滨工业大学 ， 材料科学与工程， 2021， 硕士

【摘要】 ZL114A是我国自主研发的可热处理铸造铝合金,该合金凭借其优良的铸造性能广泛的应用于制造航空发动机机匣这类结构复杂的大尺寸构件。但受到铸造工艺本身的限制,机匣铸件长期以来存在铸造缺陷多、力学性能差的问题,这些问题的出现导致机匣成品率低,制造成本居高不下,更为严重的是ZL114A本身力学性能较差,机匣服役过程中事故率和返修较高,严重威胁我国航空飞行器的使用安全,制约着飞行器性能的进一步提升。因此机匣性能改善和铸造缺陷修复成为了亟待解决重要问题,本研究在国家“两机专项”的支持下,重点研究ZL114A的热处理优化和铸造缺陷的补焊方法。采用热处理的方法进行机匣性能提升,研究了热处理工艺制度对组织和性能的影响规律以及时效过程析出相的强化机理。发现导致ZL114A强度低下的主要原因是晶界处连续分布的片状Si严重割裂铝基体,固溶处理后片状共晶Si发生球化,材料强度和塑性都有显著提升;时效过程中析出的β’’相,强化效果最好,过高的时效温度和过长的时效时间均会导致过时效的出现。在此基础上,利用响应曲面法进行热处理参数优化,发现最佳的热处理工艺制度应为:固溶540℃/12.7h+时效177.6℃/9.1h,此时ZL114A抗拉强度为357MPa,相比于热处理前(121MPa)抗拉强度提升了约190%。同时伸长率为5.6%。基于实际铸造缺陷的尺寸规格化设计了四种类型的开口,使用手工TIG焊对铸造缺陷开口进行补焊,研究焊接工艺参数对焊缝成形、接头组织和力学性能的影响规律,研究表明补焊开口的尺寸会影响焊接工艺的选择,对于Φ10mm-5mm开口最佳焊接工艺为焊接电流240A、单层补焊;Φ20mm-10mm开口的最佳焊接电流为220A,分两道次补焊;Φ25mm-20mm开口在补焊时存在焊具干涉问题,不能获得成形良好的接头,需要扩大尺寸至Φ40mm-20mm才能进行正常焊接,此时对应的焊接电流为220A,为了避免接头弱化,需要分5道次焊接。Φ10mm-5mm、Φ20mm-10mm和Φ40mm-20mm三种补焊接头焊缝区的强度较为接近且均高于母材,分别为220.3MPa、210.4MPa和215MPa,对补焊接头进行热处理后,焊缝和母材的力学性能均明显提升,两者间的强度差异减小,补焊接头的力学性能更加一致。更多还原

【Abstract】 ZL114A is a heat-treated cast aluminum alloy independently developed in China.It is widely used in manufacturing large-scale components such as aeroengine gearbox with its excellent casting properties.However,due to the limitation of casting process,there are many casting defects and poor mechanical properties of the gearbox castings for a long time.The occurrence of these problems leads to the low yield of the gearbox,high manufacturing cost,and more serious is the poor mechanical properties of ZL114 A itself,the high accident rate and repair rate during the service of the gearbox,which seriously threatens the safety of the aviation aircraft in China.It restricts the further improvement of the performance of the aircraft.Therefore,the improvement of gearbox performance and casting defect repair have become an important problem to be solved.Under the support of the national "two machine special",the project focuses on the optimization of ZL114 A heat treatment and the repair welding method of casting defects.In this paper,the performance of the gearbox is improved by heat treatment method.The influence of heat treatment process on the structure and performance and the strengthening mechanism of precipitates during aging process are studied.It is found that the main reason for the low strength of ZL114 A is that the continuous distribution of sheet Si in the grain boundary seriously splits the aluminum matrix.After solid solution treatment,the lamellar eutectic Si spheroidization occurs,and the material strength and plasticity are significantly improved;Precipitated during aging β’’ The results show that the effect of strengthening is the best.The over aging temperature and the long time of aging will lead to the over aging.On this basis,the response surface method was used to optimize the heat treatment parameters.It was found that the best heat treatment process system should be 540 ℃ /12.7h +177.6℃/9.1h solid solution,and then the tensile strength of ZL114 A was 357 Mpa,which was about 190% higher than that before heat treatment(121MPa).The elongation was 5.6%.Based on the size specification of the actual casting defects,four types of openings are designed.The manual TIG welding is used to repair the casting defects.The influence of welding process parameters on the weld forming,joint structure and mechanical properties is studied.The results show that the size of the repair weld opening will affect the selection of welding process and the selection of welding process.The best welding process for the opening of Φ10 mm-5mm is 240 A welding current and single layer repair welding;The best welding current of the opening ofΦ20mm-10 mm is 220 MPa,and it is repaired in two times;The interference problem of welding tool exists in the repair welding of Φ25mm-20 mm opening,so it is impossible to get well formed joint.It is necessary to expand the size to the normal welding can only be carried out in Φ40mm-20 mm.At this time,the corresponding welding current is 220 MPa.In order to avoid weakening of joints,5 welding times are required.The strength of the weld area of the three kinds of repair welding joints(Φ10mm-5mm,Φ 20mm-10 mm and Φ40mm-20mm)is close and higher than the base metal,respectively 220.3MPa,210.4MPa and 215 MPa.After heat treatment of the joint,the mechanical properties of the weld and the base metal are significantly improved,the strength difference between the two is reduced,and the mechanical properties of the joint are more consistent.更多还原