Effect of ultrasonic field treatment on degassing of 2024 alloy

The 2024 aluminum alloy was prepared with different ultrasonic processes. Effects of ultrasonic treatment parameters including ultrasonic power, treatment time, treatment temperature, and frequency resonance, as well as C₂Cl₆ degasser on degassing of the 2024 aluminum alloy were investigated. Results indicate that increasing ultrasonic power at the same ultrasonic treatment time can improve the degassing effect. The optimum degassing efficiency can be obtained under the resonant ultrasound condition. With the combination of 1% C₂Cl₆ addition and 150 W ultrasonic treatment for 40 s, the hydrogen content of the alloy is decreased by 52.9%. At the same time, the tensile strength and elongation are increased by 28.3% and 92.3%, respectively, and the yield strength is slightly increased by 6.7%. The degassing mechanism is also discussed.

     

微观组织对A201铝合金铸件机械性能之研究

系统改变A201铝合金平板铸件的长度、厚度及冒口大小,探讨微观组织中微孔隙量及树枝状晶胞尺寸(DCS)对A201铸件抗拉强度及伸长率的影响程度,进而于铸造实务工作时,可为冒口设计及金属凝固之参考,为研究的目的。砂型的种类有三种,分别是100%石英砂的A类石英砂、50%石英砂及50%铬砂的B类、及100%铬砂的C类。实验结果显示,A201铝合金平板铸件的机械性质同时受空孔量及DCS之影响,当微孔隙量增加及DCS变大时,均会降低铸件的抗拉强度及伸长率,其中微孔隙量影响为主要的因素。     

热处理对选区激光熔化GH3536合金晶界与拉伸行为的影响

采用选区激光熔化制备了GH3536合金,并分别进行固溶处理和热等静压处理,研究不同热处理手段对GH3536合金的组织形貌、晶界形态及室温拉伸行为的影响。结果表明:沉积态试样的组织由超细柱状亚晶粒与熔池界组成,存在气孔与微裂纹等缺陷;选区激光熔化试样分别经固溶处理和热等静压处理后,二者致密度均上升,组织转变为由交替分布的大小不等等轴晶粒组成,但热等静压的沿晶界析出M_(23)C_6相,形成锯齿状的弯曲晶界;沉积态试样的拉伸性能表现出各向异性的特点,固溶处理可消除拉伸性能的各向异性,但抗拉强度和屈服强度均有下降,延伸率明显上升。热等静压态试样与固溶态试样相类似,但其抗拉强度、屈服强度和延伸率均有进一步的提高;3种形态合金的断裂机制均为微孔聚集型的韧性断裂。     

压头速度对触变模锻原位Mg2Sip/AM60B复合材料显微组织与拉伸性能的影响(英文)

研究压头速度对Mg2Sip/AM60B复合材料显微组织和拉伸性能的影响,并与金属型铸造复合材料进行对比。结果表明,压头速度通过改变二次凝固行为和半固态变形机制对复合材料的显微组织产生明显影响,显微组织和变形机制的改变使复合材料的拉伸性能和断裂机制发生变化。当压头速度为60 mm/s时,复合材料获得最优的综合拉伸性能,抗拉强度和伸长率分别为198 MPa和10.2%。触变成形复合材料的优异性能归因于缺陷的消除和加工硬化。     

Development of high plasticity Al-Si alloy and its casting process

Aiming to meet the challenge of the shape complexity and high plasticity demanded for the upper connective plate(UCP) in motorcycle,a high plasticity Al-Si alloy named HGZL-02 was developed by optimizing the chemical composition and casting process,Premium UCP castings were obtained by using optimized casting process,Results show that fine and dense microstructure are obtained in the UCP castings,An average of 224 MPa in ultimate tensile strength,149MPa in yield strength and 13.2% in elongation are achieved for T6 heat-treated UPS castings.     

Microstructure evolution and mechanical properties of Mg-12Zn-2Y alloy containing quasicrystal phase fabricated by different casting processes

Although icosahedral quasicrystal phase (denoted as I-phase) has been verified as an outstanding reinforcing phase, the mechanical properties of quasicrystal-reinforced Mg-Zn-Y alloys fabricated by traditional casting processes are still unsatisfactory due to the serious segregation of intermetallic compounds. In this study, the microstructure and mechanical properties of Mg-12Zn-2Y alloy fabricated by different casting processes, including permanent mold casting, squeeze casting and rheo-squeeze casting with ultrasonic vibration, were systematically investigated and compared. The results show that massive, large-sized I-phase and Mg₇Zn₃ phase gather together in the permanent mold cast sample, while the squeeze casting process leads to the transformation of I-phase into fine lamellar morphology and the amount of Mg₇Zn₃ decreases. As to the rheo-squeeze casting process, when the ultrasonic vibration is exerted with power from 800 W to 1,600 W, the α-Mg grains are refined and spheroidized to a large extent, and the lamellar spacing of the eutectic structure is significantly reduced, accompanied by some tiny granular I-phase scattering in the α-Mg matrix. However, when the ultrasonic power continuously increases to 2,400 W, the eutectic structure becomes coarse. The best mechanical properties of the rheo-squeeze cast alloy are obtained when the ultrasonic power is 1,600 W. The microhardness, yield strength, ultimate tensile strength and elongation are 79.9 HV, 140 MPa, 236 MPa, and 3.25%, which are 44.1%, 26.1%, 25.5%, 132.1% respectively higher than the corresponding values of the squeeze casting sample, and are 47.6%, 44.3%, 69.8%, and 253.3% respectively higher than the corresponding values of the permanent mold casting sample.

     

Effects of filter materials on microstructure and mechanical properties of AZ91

The present investigation studied the effects of different kinds of ceramic foam filters (CFF) incorporating gas bubbling on the microstructure and mechanical properties of virgin AZ91 alloys, and the reactions between filters and Mg melt during filtration. The results show that the purification process of CFF incorporating gas bubbling process can obviously improve the R m and A of AZ91 alloy, especially the A. Amongst the selected four kinds of CFF, the MgO filter is the most suitable for filtrating Mg melt, and the filtration effective sequence of four kinds of filtrating materials is as follows: MgOAl2O3ZrO2SiC. With MgO filter incorporating gas bubbling treatment under Ar flow rate of 2 L/min and temperature of 730 °C, the ultimate tensile strength R m and elongation A can be improved greatly from 175.3 MPa and 2.74% to 195.4 MPa and 4.54%, respectively. No inclusions are found on the fracture surface of the sample filtrated by MgO ceramic foam filter, and the fracture mode is quasicleavage crack.     

Effect of Sb on microstructure and mechanical properties of Mg2Si/Al-Si composites

The effect of Sb on the microstructure and mechanical properties of Mg2Si/Al-Si composites was investigated.The results show that Sb can improve the microstructure and mechanical properties of Mg2Si/Al-Si composites.When the content of Sb is 0.4%,the morphology of primary Mg2Si changes from dendrites to fine particles,the average size of Mg2Si particles is refined from 52 to 25μm,and the ultimate tensile strength and elongation of the composites increase from 102.1 MPa and 0.26% to 138.6 MPa and 0.36%,respectively.The strengthening mechanism can be attributed to the fine-grain strengthening.However,excessive Sb is disadvantageous to the modification of the composites.     

Study on the Mechanical Properties of Cast 6063 Al Alloy Using a Mixture of Aluminum Dross and Green Sand as Mold

The mechanical characteristics of 6063 aluminum alloy cast in a mixture of aluminum dross and silica sand as mold have been examined. The amount of dross in the green silica sand was varied in the range of 0?C80% with bentonite as binder. In all, 40 samples were cast, and 8 of these were left in the as-cast condition for control while 32 were first homogenized at 470°C for 6?h and then rolled in a two-high mill at ambient temperature to 10% reduction in one pass. The rolled samples were solution heat treated at 515°C for 8?h followed by normalizing, annealing, and quench tempering, respectively. The samples were then simulated and tensile behavior coupled with the evaluation of microhardness and microstructures developed. The results obtained demonstrate significant improvement in mechanical properties from 50% to 80% dross in the mold. Tensile strength increased to 177?MPa and 15% elongation compared with conventional 6063-T5 aluminum alloy with 145?MPa tensile strength and 8% elongation. The improvement in mechanical properties by the quench-tempered samples can be attributed to the inducement of fine and coherent Mg₂Si crystals within the matrix. Furthermore, the overall analysis of the proportion of dross to the size of cast show that about 64% of dross generated can be utilized as mold material.     

Hydrogen,bifilms and mechanical properties of Al castings

Recent research has suggested that H dissolved in an Al melt could diffuse into double oxide films (bifilms), increasing their size and forming oxide related hydrogen containing porosity, which was found to decrease the Weibull moduli of the tensile properties of castings. In this work, the Weibull moduli of the tensile properties of two Al castings, both expected to contain oxide films of approximately the same amount and age, were compared. The results showed that, when the H content of the castings was reduced to ～50%, from 0·18 to 0·08 cm³/100 g Al, there was an increase in the Weibull moduli of the ultimate tensile strength (UTS) and the % elongation by ～400% and 200% respectively. The increased Weibull modulus was thought to be brought about by holding the moulds under vacuum and thus reducing H pick-up by the metal, from the solvent and the resin in the sand moulds.     

Effects of C<Subscript>2</Subscript>Cl<Subscript>6</Subscript> addition on grain refinement and mechanical properties of AZ31 magnesium alloy

Grain refining effects of C₂Cl₆ addition were investigated using AZ31 magnesium alloy. The addition of C₂Cl₆ to AZ31 magnesium alloy significantly reduced the grain size from 280 μm to about 120 μm, and the tensile properties were also increased due to grain refinement. EPMA analysis showed that apparent segregation of carbon element occurred in AZ31 castings treated with carbon. It was considered that the carbon might also have strong segregating power that restricts the grain growth and affects the constitutional undercooling, which in turn results in grain refining effects.     

Microstructures and mechanical properties of semi-solid squeeze casting ZL104 connecting rod

Semi-solid squeeze casting (SSSC) and liquid squeeze casting (LSC) processes were used to fabricate a ZL104 connecting rod, and the influences of the process parameters on the microstructures and mechanical properties were investigated. Results showed that the tensile strength and elongation of the SSSC-fabricated rod were improved by 22% and 17%, respectively, compared with those of the LSC-fabricated rod. For SSSC, the average particle size (APS) and the shape factor (SF) increased with the increase of re-melting temperature (T_r), whereas the tensile strength and elongation increased first and then decreased. The APS increased with increasing the mold temperature (T_m), whereas the SF increased initially and then decreased, which caused the tensile strength and elongation to increase initially and then decrease. The APS decreased and the SF increased as squeezing pressure (p_s) increased, and the mechanical properties were enhanced. Moreover, the optimal T_r, p_s and T_m are 848 K, 100 MPa and 523 K, respectively.     

Effects of CeO2 additive on the microstructure and mechanical properties of in situ TiB2/Al composite

In this paper, CeO₂ was investigated as an additive for in situ preparation of TiB₂/Al composite using an exothermic reaction process via K₂TiF₆ and KBF₄ salts. Experimental results indicated that when 0.5 wt.% CeO₂ additive was added, the dispersion of TiB₂ particles was improved significantly. Meanwhile, α-Al matrix grain was further refined. Compared with the composite without CeO₂, the ultimate tensile strength, yield strength, elastic modulus and tensile elongation increased by 8%, 7%, 26% and 14%, respectively in as-cast condition, and the tensile fracture behavior of the composite with CeO₂ belonged to a typical ductile fracture with microvoid coalescence.     

Effects of Er on the microstructure and properties of AZ31 magnesium alloy prepared via the EMS process

The effects of small amounts of the rare-earth element erbium on the microstructure and the mechanical properties of AZ31 magnesium alloy via the electromagnetic stirring(EMS) process have been studied.It has been shown that AZ31-Er alloys are mainly composed of α-Mg solid solution and β-Mg17Al12 phases.When the Er content reaches 0.12 wt.%,the characteristic peaks of Al2Er can be observed.The micro-structure is obviously refined and the tensile strength of the AZ31-based alloy at ambient temperature is significantly improved by contents of 0.03 wt.% Er,especially the elongation(δ=19%).More addition of Er obviously decreases the tensile strength and elongation of the AZ31-based alloy because of the grain coarsening and the reduction of β-Mg17Al12 phases.     

不同压力下挤压铸造铝铜合金的组织与性能

采用挤压铸造工艺制备出一种新开发的、高强韧铝铜合金.T5热处理状态下其抗拉强度达到433 MPa,伸长率为14%.通过对该合金力学性能及其显微组织的研究表明,铸态和经T5热处理的抗拉强度和伸长率均随压力的增加而增大,在压力为50MPa时达到最大值,但在铸态下,未加压力的铸造合金其硬度高于挤压铸造的合金硬度.随挤压力增加,晶粒明显细化,二次枝晶增加,枝晶间距减小.     

Studies on eutectic Al–Si alloy–flyash composites

Abstract

In this investigation, an attempt was made to study the influence of melt treatments like grain refinement and modification on the mechanical properties of cenospheres of flyash–LM6 composites. Stir casting route was employed to disperse the flyash (1–15?wt‐%) in the LM6 alloy matrix. For each percentage of flyash, melts were subjected to grain refinement, modification or combined grain refinement and modification. The results reveal that castings subjected to melt treatments showed increased hardness, ultimate tensile strength and elongation compared with untreated Al–Si base alloy up to 10% flyash. Addition of flyash beyond 10% resulted in decreases in hardness and ultimate tensile strength. Percentage elongation showed a decreasing trend for all the cases studied. Nevertheless, in all the cases studied, mechanical properties were higher than that of the Al–Si base alloy. Among all the composites, the best results were obtained with 10% flyash subjected to modification alone.     

Effects of Cooling Rate on High-temperature Mechanical Properties of A356 Alloys

High temperature mechanical properties of A356 alloy castings under different solidification cooling rates have been studied and the influence of cooling rates on secondary dendrite arm spacing (SDAS) and mechanical properties has been discussed. To get different cooling rates, three different types of mold—green sand, green sand with chill and permanent mold, were used to pour castings which would subsequently be machined into tensile test and metallographic specimens. The temperature curves of castings’ solidification in three different mold were recorded using thermal couples, which would be used to calculate their corresponding cooling rates. Tensile tests were carried out at 20, 200, 300, 400 and 500 ℃ and then mechanical properties, such as tensile strength, yield strength, elongation, of specimens from different mold types at different test temperatures were obtained. And SDAS of different specimens were measured using optical metallographic photos. From integrated analysis of all those results, following conclusions could be reached. The relationship between SDAS and cooling rates is negative, and the quantitative relationship has been obtained through data fitting analyzing. Generally speaking, tensile strength and yield strength decease as the temperature elevates while elongation behaves in the contrary trend. Through the regression analysis of SDAS, mechanical properties and temperature, the relationship among them is obtained, which makes quantitative prediction of A356 alloy’s mechanical properties at different temperatures with different solidification cooling rates be possible.     

Mg-Zn-Y-Nd-Zr合金的显微组织、织构、力学性能

对Mg-Zn-Y-Nd-Zr合金的显微组织和力学性能进行了研究。结果表明,Nd元素的加入部分取代了W相（Mg₃Zn₃Y₂）中的Y元素,形成了新的第二相Mg₃Zn₃(Y, Nd)₂。热挤压后观察到由细小的等轴再结晶晶粒和粗大的细长未再结晶晶粒组成的典型双峰结构。Nd元素的加入促进了热挤压过程中的动态再结晶,随着Nd含量的增加,动态再结晶率增加,挤压态合金的整体织构强度减弱。Nd的加入细化了晶粒并改善了合金的力学性能。添加0.5%（质量分数）Nd时,挤压态合金表现出高强度和高塑性的良好结合：屈服强度为362 MPa,极限抗拉伸强度为404 MPa,延伸率为10.2%。时效处理后合金的抗拉伸强度进一步提高,峰值时效极限抗拉伸强度可达421 MPa。合金的高强度主要归功于超细再结晶晶粒和析出强化。     

Effect of short-term tempering on microstructure and mechanical properties of high-strength FeCrMoVC

The present work describes a systematic investigation of the influence of short-term tempering on the microstructure and mechanical properties of a fast solidified Fe_84.3Cr_4.3Mo_4.6V_2.2C_4.6 (at.%) alloy. The applied casting conditions promote the formation of non-equilibrium phases such as martensite, retained austenite and a complex network of fine carbides already in the as-cast state. Additional short-term tempering further increases the strength and hardness of the alloy along with significantly improved ductility under compressive and tensile loading. By this procedure an extremely high ultimate compression strength of almost 4500 MPa combined with a compressive fracture strain of ～22% and an ultimate tensile strength of over 1600 MPa can be achieved. The interacting mechanisms appearing due to short-term tempering were investigated by different X-ray diffraction methods and Auger electron spectroscopy, and a transformation of austenite into martensite as well as the formation of nano-carbides and a change in residual stresses during tempering was detected. Altogether, the outstanding properties of the material combined with the energy-efficient manufacturing process for Fe_84.3Cr_4.3Mo_4.6V_2.2C_4.6 open up a new possibility to obtain a high-strength and simultaneously adequately ductile alloy for advanced tool design.     

Performance of tungsten fibers for Wf/W composites under cyclic tensile load

Toughness improved tungsten-based composites are one of the currently considered material option for future fusion reactors capable to withstand both high heat flux and irradiation induced embrittlement. Today, fiber-reinforced composites (W_f/W) are being intensively studied as risk-mitigation materials to replace bulk tungsten which is susceptible to neutron irradiation embrittlement especially below 800 °C. Operation of a material as an element of a plasma facing component (i.e. divertor monoblock or first wall armour) implies not only high heat flux exposure but also thermal cyclic fatigue caused by repetitive oscillations of the heat loads due to the nature of the plasma and the limitations on the capacity of its confinement. In this work, we assessed the performance of potassium doped tungsten fibers under cyclic loading applied in tensile mode. Stress-controlled fatigue tests were performed at room temperature, 300 °C and 500 °C increasing the load from 50% of the yield strength up to the ultimate tensile strength of the studied fibers. It is revealed that significant cyclic hardening emerges as the fatigue stress limit exceeds the yield strength already within a few cycles. Despite the noticed cyclic hardening, the wire can sustain few hundreds of cycles without any detectable damage unless the cycle stress is increased to reach the value above the mean ultimate tensile strength. Given this observation, we have studied the impact of the cyclic stress (σ_C) on the rupture strength and total elongation of the wires exposed to twenty loading cycles varying test temperature in the range 23–500 °C. At room temperature, the rupture stress after cyclic deformation progressively increases with σ_C and saturates at 2.7 GPa with a moderate reduction of the total elongation, while the nominal ultimate tensile strength of the wire is 2.5 GPa. Thus, the strength of the wire is increased by 200 MPa, on average. At elevated temperature, the rupture stress after the cyclic deformation increases by more than 300 MPa.