真空增压铸造工艺对ZL114A合金充型能力和力学性能的影响

目的 研究不同真空增压铸造工艺参数下ZL114A合金的充型距离、组织性能的变化规律。方法 设计了不同厚度的充型距离测试片,采用游标卡尺测试了不同真空度和石膏铸型温度条件下合金的流动性。采用万能拉伸机测试了不同凝固压力条件下单铸试棒的力学性能,采用金相显微镜观察合金的显微组织,采用扫描电子显微镜观察拉伸断口的形貌。结果 当真空度从重力状态(0 MPa)提高至-0.08 MPa时,3.0 mm薄片的充型距离从42 mm提升至210 mm。当铸型温度从260℃提高至340℃,3.0 mm薄片的充型距离从95 mm提升至175 mm。凝固压力从重力条件下提升至0.8 MPa,抗拉强度从293 MPa提升至338 MPa,屈服强度从240 MPa提升至278 MPa,断后伸长率从2.0%提升至4.0%。结论 提高真空度、铸型温度,可显著提升ZL114A合金的充型能力。提高凝固压力、凝固组织致密,第二相分布均匀,疏松缺陷明显减少,力学性能提高。     

合金成分对定向凝固柱晶高温合金热裂倾向性的影响

为研究定向凝固柱晶高温合金薄壁铸件凝固过程的热裂纹形成倾向,采用定向凝固空心薄壁管状试样,考察了Ti,Zr,Hf,Al和B等元素对定向凝固柱晶高温合金热裂倾向性的影响;采用SEM、断口分析及DSC方法,分析了热裂的晶界宏观形态.结果表明:随着Ti含量的增加,γ/γ′共晶增多,尺寸增大,合金凝固温度范围变大,定向合金的热裂倾向性严重;Zr元素含量增加,促成共晶形成,合金出现热裂纹;Hf含量的变化对合金的热裂没有影响;Al,B含量增加,微观组织无明显变化,但合金凝固温度范围变大,导致定向凝固合金出现热裂.     

浇注温度对定向凝固Al－Cu合金热裂的影响

针对空心叶片类定向凝固铸件存在的热裂问题，开展了定向凝固热裂规律的研究。本文选择凝固参数较全的Ａｌ－Ｃｕ系合金，研究了定向凝固工艺参数之一的浇注温度对Ａｌ－０．６ｗｔ％Ｃｕ和Ａｌ－２．０ｗｔ％Ｃｕ合金热裂的影响。定向凝固热裂试验表明，提高浇注温度可以降低Ａｌ－０．６ｗｔ％Ｃｕ合金的热裂程度，但对Ａｌ－２．０ｗｔ％Ｃｕ则无作用。理论分析认为，合金在不可补缩区的冷却速率变化是改变合金热裂程度的重要因素。     

浇注温度对定向凝固Al－Cu合金热裂的影响EI

针对空心叶片类定向凝固铸件存在的热裂问题，开展了定向凝固热裂规律的研究。本文选择凝固参数较全的Ａｌ－Ｃｕ系合金，研究了定向凝固工艺参数之一的浇注温度对Ａｌ－０．６ｗｔ％Ｃｕ和Ａｌ－２．０ｗｔ％Ｃｕ合金热裂的影响。定向凝固热裂试验表明，提高浇注温度可以降低Ａｌ－０．６ｗｔ％Ｃｕ合金的热裂程度，但对Ａｌ－２．０ｗｔ％Ｃｕ则无作用。理论分析认为，合金在不可补缩区的冷却速率变化是改变合金热裂程度的重要因素。     

汽车增压器涡轮用铸造高温合金热裂研究进展

采用高温合金浇注汽车增压器涡轮时,叶片极易产生热裂,热裂的存在严重影响了铸造高温合金在增压涡轮上的使用。介绍了几种目前国内广泛使用的汽车增压器涡轮用铸造高温合金,对铸件热裂的形成机理进行了综述,重点探讨了铝、钛、碳、锆和铪等元素对铸造高温合金热裂倾向性的影响。综述了合金凝固方式和铸型性质、浇注条件、铸件结构、浇注系统等铸造工艺参数对热裂的影响,并提出了防止热裂产生的措施。     

铸造工艺对K424合金涡轮组织和性能的影响

研究了不同铸造工艺对K424合金涡轮铸件组织和性能的影响,实验结果表明:浇注温度和模壳温度越高,铸件晶粒越大,越容易在靠近浇口部位产生缩孔缺陷;反之,晶粒越小,组织越均匀,铸件成型和补缩越困难,内部显微疏松越严重,力学性能波动越大;通过采用一定的强化控制凝固冷却措施,有利于涡轮铸件轮盘部位的凝固补缩.当模壳温度为950℃、浇注温度为1470℃,并采用适当的强化控制凝固冷却措施时,K424合金涡轮铸件获得较理想的显微组织、优良的综合力学性能.     

镁合金热裂行为研究的测试方法探讨

针对镁合金的特点，就合金热裂行为研究的测试方法进行了实验研究和分析。用热裂行为测试系统测量合金凝固过程中的温度、线收缩和收缩应力，用铸造热分析系统分析铸造凝固条件下的相析出，这为研究合金的热裂形成机理提供了重要的实验手段。采用热裂环法可以有效地评价合金的热裂倾向性，而等长度试棒法(无论金属型还是砂型)则不适于测试镁合金。     

铝(镁)合金消失模铸造近净成形技术研究进展

阐述了铝(镁)合金消失模铸造技术的研究现状,着重介绍了铝(镁)合金消失模铸造在金属液充型、振动凝固、压力凝固以及消失模壳型铸造等技术方面的最新研究进展。研究表明,铝(镁)合金在消失模铸造过程中,需重点解决针孔、缩松等缺陷,提高液态合金的充型能力和铸件的力学性能;通过采用振动凝固和压力凝固的手段,可以提高金属液充型能力、细化组织、提高组织致密性,明显提高铸件力学性能。真空低压消失模壳型铸造技术,可以解决普通消失模铸造易于出现的孔洞和夹杂等缺陷以及浇不足和浇注温度高等问题,是一种生产复杂薄壁高质量铝、镁合金精密铸件的新方法。     

Mg-Gd-Y合金及其构件的组织与性能研究

目的 针对VW103(Mg-10Gd-3Y)和VW63(Mg-6Gd-3Y)2种铸造镁合金,从材料微观结构入手,探讨分析2种合金力学性能差异性,获取了2种镁合金在工程应用中的铸造性能及其力学特性。方法 采用热分析法和改进的裂纹环试样等方法,开展2种合金的凝固温度范围和铸造裂纹倾向研究。测量和分析其凝固温度范围、液态流动性、热态和冷态下的材料抗裂性能,获得Mg-Gd-Y稀土铸造镁合金的铸造特性;基于构件本体不同区域取样,获得Mg-Gd-Y合金在室温和150℃下的力学性能,并对整体铸件结构的承载能力和稳定性进行评估。结果 在铸造性能方面,热态下脱模,VW103和VW63 2种合金均未出现开裂现象;冷态下脱模,VW103合金试样出现开裂。在力学性能方面,与VW103合金相比,VW63合金具有更好的综合力学性能,VW63合金铸件本体试样在高温（150℃）条件下拉伸性能均值为320 MPa,表现出优异的力学性能。结论 VW63合金具有更好的力学性能和铸造性能,采用VW63合金、树脂砂反重力方法制备的整体铸件满足了结构承载能力需求,并且在测试过程中铸件位移（变形）与载荷和加载时间呈现出良好的线性关...     

TC4钛合金与Nb-W-Mo-Zr铌合金的真空电子束焊接工艺研究

采用真空电子束焊对TC4钛合金和Nb-W-Mo-Zr 铌合金进行了成功焊接,焊接的基本工艺参数为:炉室真空度≤3.0×10-2 Pa,枪室真空度≤1.5×10-3 Pa,焊接电压56～60 kv,束流20～25 mA,工件的移动速度为550～600 mm/min.用扫描电镜对焊接组织进行了观测,并作了X射线无损探伤.结果表明,热影响区和熔合区组织致密,焊缝熔透性好,无气孔.熔合区主要为胞状柬凝固结构,基本无枝晶出现.X射线探伤结果得出,焊缝质量满足国家一级标准.焊接组件在室温下的力学性能为:Rm=595 MPa,RP0.2=482 MPa,A=20%,Z=63%.     

Effects of processing parameters on microstructure and mechanical properties of squeeze-cast Mg–12Zn–4Al–0.5Ca alloy

In this paper, a new magnesium alloy Mg–12Zn–4Al–0.5Ca (ZAX12405) was prepared by squeeze casting. The effects of processing parameters including applied pressure, pouring temperature and dwell time on the microstructure and mechanical properties of squeeze-cast ZAX12405 alloy were investigated. It was found that squeeze-cast ZAX12405 alloy exhibited finer microstructure and much better mechanical properties than gravity casting alloy. Increasing the applied pressure led to significant cast densification and a certain extent of grain refinement in the microstructure, along with obvious promotion in mechanical properties. Lowering the pouring temperature refined the microstructure of ZAX12405 alloy, but deteriorated the cast densification, resulting in that the mechanical properties firstly increased and then decreased. Increasing the dwell time promoted cast densification and mechanical properties just before the solidification process ended. A combination of highest applied pressure (120 MPa), medium pouring temperature (650 °C) and dwell time (30 s) brought the highest mechanical properties, under which the ultimate tensile strength (UTS), yield strength (YS) and elongation to failure (E_f) of the alloy reached 211 MPa, 113 MPa and 5.2% at room temperature. Comparing with the gravity casting ZAX12405 alloy, the UTS and E_f increased 40% and 300%, respectively. For squeeze-cast Mg–12Zn–4Al–0.5Ca alloy, cast densification was considered more important than microstructure refinement for the promotion of mechanical properties.     

Ti-3Al-2.5V钛合金精密铸造浇注系统优化研究

利用数值模拟方法,研究了重力场和立式离心场下,不同浇注系统（顶-底、螺旋、径向和树形系统）Ti-3Al-2.5V钛合金铸件的充型和凝固过程及缩孔缺陷分布规律,并通过实际铸造实验,对铸件的机械性能及缩孔缺陷进行了检测。结果表明,重力场下的顶-底浇注系统氧含量波动范围大,不同浇注系统对合金力学性能影响不大,缩孔的模拟结果与实际铸造情况都吻合较好。相比而言,重力场下由于金属液的紊流更容易形成夹杂、钛豆、缩孔等缺陷,而离心场下由于离心力的作用,形成缩孔等缺陷的数量相对较少。     

Study on squeeze casting of an in situ 5 vol.-% TiB2/2014 Al composite

Abstract

An in situ 5 vol.-% TiB₂/2014 composite was prepared by an exothermic reaction of K₂TiF₆, KBF₄ and Al melts. The effect of introduction of in situ formed TiB₂ particles on the squeeze-casting formability of the composite was discussed. The microstructural evolution and changes in the mechanical properties of the composite at different squeeze pressures were investigated. The results showed that a pouring temperature of 710°C, a die temperature of 200°C and a squeeze pressure of 90 MPa were found to be sufficient to get the qualified squeeze cast and maximum mechanical properties for an Al 2014 alloy. However, the pouring temperature, die temperature and squeeze pressure need to be increased to 780°C, 250°C and 120 MPa for the composite to get the qualified squeeze cast and maximum mechanical properties as a result of the effect of introduction of in situ formed TiB₂ particles on the solidification process, plasticity and fluidity of the composite. The microstructural refinement, elimination of casting defects such as shrinkage porosities and gas porosities and improved distribution of TiB₂ particles in the case of the composite result when pressure was applied during solidification. Compared with the gravity-cast composite, the tensile strength, yield strength and elongation of the squeeze-cast composite at 120 MPa increased by 21%, 16% and 200%.     

Effect of post-weld aging treatment on mechanical properties of Tungsten Inert Gas welded low thickness 7075 aluminium alloy joints

This paper reports the influence of post-weld aging treatment on the microstructure, tensile strength, hardness and Charpy impact energy of weld joints low thickness 7075 T6 aluminium alloy welded by Tungsten Inert Gas (TIG). Hot cracking occurs in aluminium welds when high levels of thermal stress and solidification shrinkage are present while the weld is undergoing various degrees of solidification. Weld fusion zones typically exhibit microstructure modifications because of the thermal conditions during weld metal solidification. This often results in low weld mechanical properties and low resistance to hot cracking. It has been observed that the mechanical properties are very sensitive to microstructure of weld metal. Simple post-weld aging treatment at 140 °C applied to the joints is found to be beneficial to enhance the mechanical properties of the welded joints. Correlations between microstructures and mechanical properties were discussed.     

铝合金汽车转向节精密铸造工艺研究

目的 对某铝合金汽车转向节的精密铸造工艺进行设计与优化研究,以得到合格的铝合金汽车转向节的精密铸造工艺方案。方法 结合铝合金转向节铸件的结构特征、铸件材料特性和铸造经验,在转向节铸件主体部和鹅颈部各开设一个内浇口,设计了铝合金转向节初始浇注方案;通过在初始工艺方案中铸件缺陷较严重的区域设置补缩冒口、在铸件顶部增设排气道等措施给出了铝合金汽车转向节的优化浇注方案,基于ProCAST软件建立了铝合金转向节精密铸造2种浇注方案的有限元模型,对铝合金转向节精密铸造的充型过程、凝固过程及缩孔缩松特性进行了数值模拟与分析。结果 铝合金转向节铸件初始浇注方案的充型过程相对稳定流畅,铸件在凝固过程中有孤立液相区的形成,完全凝固后铸件中间部位存在大面积缩松缩孔缺陷;优化浇注方案能够控制金属液的流动、充型顺序及凝固特性,铸件的整个凝固过程基本呈中间对称分布,最后凝固区域位于补缩冒口内部,最大缩孔缩松率控制在2%以下。结论 优化浇注方案的设计合理且有效,能够有效地消除铝合金转向节铸件的缺陷。     

热等静压工艺参数对ZTC4钛合金力学性能的影响

为了使ZTC4钛合金铸件具有较优的力学性能,系统地研究了热等静压温度、时间、压力等工艺参数对ZTC4钛合金铸板力学性能的影响.结果表明:热等静压工艺参数变化对ZTC4钛合金室温拉伸性能、弯曲性能都有影响,其中对ZTC4钛合金伸长率的影响最为明显,但对冲击性能影响不显著.综合考虑各因素,在920℃/125MPa/2h热等...     

Studies on squeeze casting of Al 2124 alloy and 2124-10% SiCp metal matrix composite

Aluminium 2124 alloy and its composite with 10% SiC particles of average particle size of 23 μm were squeeze cast at different pressures. The effect of squeeze pressure during solidification was evaluated with respect to microstructural characteristics using optical microscopy and image analysis and mechanical properties by tensile testing. The microstructural refinement, elimination of casting defects such as shrinkage and gas porosities and improved distribution of SiC particles in the case of the composite were resulted when pressure is applied during solidification. A pressure level of 100 MPa was found to be sufficient to get the microstructural refinement and very low porosity level in both the alloy and the composite. The improved mechanical properties observed in the squeeze cast alloy and the composite could be attributed to the refinement of microstructure within the material.     

Density and Mechanical Properties of Aluminum Lost Foam Casting by Pressurization during Solidification

Porosity is thought to be severe in aluminum alloy castings produced by lost foam process due to the pyrolysis of the polystyrene foam pattern during pouring, which results in detrimental effect in mechanical property. The slow solidification rate promotes the formation of gassing pin holes, and relative weakness of the thermal gradients can cause micro-shrinkage if the outline of the part complicates feeding in the lost foam casting. One of the methods to eliminate the porosity is to apply high pressure to the molten metal like an isostatic forging during solidification. Fundamental experiments were carried out to evaluate the effect of the external pressure on the porosity and mechanical properties of A356.2 alloy bar in the lost foam casting. Solidification time and porosity decreased with increasing the applied pressure during solidification. Applying external pressure was effective in decreasing the porosity and increasing the elongation of the lost foam casting.