Effects of casting speed on microstructure and segregation of electromagnetically stirred Aluminum alloy in continuous casting process

Recently, a semi-solid metal processing has been acknowledged as a cost-effective technique to be able to manufacture high quality product for the transportation industry.In this study a hypo-eutectic Al alloy was fabricated by means of an electromagnetic stirrer in continuous casting process and the microstructural change during solidification due to a fluid flow by electromagnetic stirring was examined.Due to the forced fluid flow during solidification a dendritic phase of primary α phase of Al alloy was turned into a globular phase, which can make the Al alloy get a thixotropic behavior in the semi-solid region.In order to establish the quantitative relationship between microstructure and the process parameters, the morphology shape, a silicon distribution and a size of primary α phase were observed according to casting speed in continuous casting machine.The primary α phase was turned into the degenerate dendrites approaching a spherical configuration with increasing casting speed.The fine-grained and equiaxed microstructure appeared at higher casting speed.A segregation behavior of Si element was declined with increasing casting speed and a very uniform distribution of Si element was observed on the billet at a casting speed of 600 mm·min-1.A thickness of the solidifying shell of the billet was shortened with increasing the casting speed.     

Microstructure,tensile properties and fractography of A356 alloy under as-cast and T6 obtained with expendable pattern shell casting process

The microstructure, tensile properties and fractography of A356 alloy were studied under as-cast and T6 conditions obtained with expendable pattern shell casting, and the results were compared with lost foam casting (LFC). The results indicate that a(Al) primary, eutectic silicon and Mg₂Si are the main phases in the microstructure of A356 alloy obtained with this casting process. The eutectic silicon particles are spheroidized and uniformly distributed at the grain boundaries after T6 treatment. The average length, average width and aspect ratio of eutectic silicon particles after T6 condition decrease. The sizes of a(Al) primary phase and eutectic silicon of this casting process are smaller than those of LFC. The tensile strength, elongation and hardness of A356 alloy after T6 obviously increase, they reach 260.53 MPa, 6.15% and 86.0, respectively and have a significant improvement compared to LFC. The fracture surfaces of expendable pattern shell casting show a mixed quasi-cleavage and dimple fracture morphology as a transgranular fracture nature. However, the fracture surfaces of LFC display a brittle fracture.     

Performance evaluation of PVD coatings for high pressure die casting

During high-pressure die-casting (HPDC) of aluminium alloys, there is a tendency for the molten alloy to react with the tool steel die, core pins and inserts. This occurrence within the high pressure die casting (HPDC) industry is referred to as ‘soldering’. It is of concern to high-pressure die casters because of down-time due to the regular removal of the soldered layer and its detrimental affect on die life and casting quality. In this investigation, several physical vapour deposited (PVD) coatings, namely, TiN, CrN and TiCN, were evaluated for their ability to eliminate soldering during HPDC of aluminium alloys. Accelerated semi-industrial trials were carried out in a 250-t Toshiba HPDC machine using a specially designed die made of P20 tool steel with removable core pins. The results from these trials showed that PVD coatings can act as a physical barrier coating preventing any reaction between the molten aluminium alloy and the tool steel. Thus the problem of soldering on such tools as core pins can be eliminated in high HPDC of aluminium alloys. In the accelerated trials, it was found that soldering was replaced by a built-up layer of cast aluminium alloy, which was less detrimental to tool life and reduced machine down-time due to the reduced need for tool polishing. The experimental results were confirmed by conducting in-plant HPDC trials.     

Effect of thermal exposure on microstructure and mechanical properties of Al−Si−Cu−Ni−Mg alloy produced by different casting technologies

The effect of thermal exposure at 350 °C for 200 h on microstructure and mechanical properties was investigated for Al−Si−Cu−Ni−Mg alloy, which was produced by permanent mold casting (PMC) and high pressure die casting (HPDC). The SEM and IPP software were used to characterize the morphology of Si phase in the studied alloys. The results show that the thermal exposure provokes spheroidization and coarsening of eutectic Si particles. The ultimate tensile strength of the HPDC alloy after thermal exposure is higher than that of the PMC alloy at room temperature. However, the TEPMC and TEHPDC alloys have similar tensile strength around 67 MPa at 350 °C. Due to the coarsening of eutectic Si, the TEPMC alloy exhibits better creep resistance than the TEHPDC alloy under studied creep conditions. Therefore, the alloys with small size of eutectic Si are not suitably used at 350 °C.     

Performance of digital patternless freeze-casting sand mould

Digital patternless freeze-casting technology is a new approach for obtaining frozen sand moulds using digital milling technology.The change law of tensile strength and air permeability of frozen sand moulds (100-mesh and 200-mesh silica sand,and zircon sand moulds) under different freezing temperatures and water contents was studied.Results show that with the decrease of freezing temperature and the increase of water contents,the tensile strength and air permeability of the sand moulds are gradually improved.Meanwhile,computed tomography technology was used to characterize the shape and size of the water film between the sand particles mixed with 4wt.% water.The results show that in silica sand moulds,the form of water film is lumpy,and 200-mesh silica sand moulds have more water films and higher proportion of small-sized water films than 100-mesh silica sand moulds,while in zircon sand moulds,the form of water film is membranous.At the same freezing temperature and water content,the tensile strength of zircon sand mould is the highest,and 100-mesh silica sand mould is the lowest.A comparative solidification experiment of A356 aluminum alloy was carried out in frozen sand mould and resin sand mould.The results show that the primary α-Al phase appears in the form of equiaxed and eutectic silicon phase is needle-like in freezing sand mould casting,but the primary α-Al phase grows in the form of dendrites,and the eutectic silicon phase is coarse needle-like in the resin sand mould casting.The difference of microstructure is caused by the different cooling rate.The cooling rate of A356 aluminum alloy in frozen sand mould is higher than that in resin sand mould.     

Defect band formation in high pressure die casting AE44 magnesium alloy

The characteristics of defect bands in the microstructure of high pressure die casting (HPDC) AE44 magnesium alloy were investigated. Special attention was paid to the effects of process parameters during the HPDC process and casting structure on the distribution of defect bands. Results show that the defect bands are solute segregation bands with the enrichment of Al, Ce and La elements, which are basically in the form of Al₁₁RE₃ phase. There is no obvious aggregation of porosities in the defect bands. The width of the inner defect band is 4–8 times larger than that of the outer one. The variation trends of the distribution of the inner and outer defect bands are not consistent under different process parameters and at different locations of castings. This is due to the discrepancy between the formation mechanisms of double defect bands. The filling and solidification behavior of the melt near the chilling layer is very complicated, which finally leads to a fluctuation of the width and location of the outer defect band. By affecting the content and aggregation degree of externally solidified crystals (ESCs) in the cross section of die castings, the process parameters and casting structure have a great influence on the distribution of the inner defect band.

     

镁合金铸造成形过程宏观／微观模拟

通过研究镁合金压铸过程中界面热,采用热传导反算法确定压铸过程的界面换热系数,研究镁合金压铸过程中工艺参数及凝固过程对铸件界面换热系数的影响规律,建立镁合金压铸过程界面换热边界条件的处理模型,以实现镁合金压铸过程中凝固过程的准确预测。通过实验研究镁合金压铸过程中凝固组织,建立了镁合金压铸过程中形核模型。采用CA方法,建立了镁合金枝晶生长模型,以实现镁合金凝固组织的预测。采用相场方法研究了镁合金枝晶生长形貌。     

Microstructure and mechanical properties of Mg-Al-Mn-Ca alloy sheet produced by twin roll casting and sequential warm rolling

Microstructural evolution and mechanical properties of twin roll cast (TRC) Mg-3.3 wt.%Al-0.8 wt.%Mn-0.2 wt.%Ca (AM31 + 0.2Ca) alloy strip during warm rolling and subsequent annealing were investigated in this paper. The as-TRC alloy strip shows columnar dendrites in surface and equiaxed dendrites in center regions, as well as finely dispersed primary Al₈Mn₅ particles on interdendritic boundaries which result in the beneficial effect on microstructural refinement of strip casting. The warm rolled sheets show intensively deformed band or shear band structures, as well as finely and homogeneously dispersed Al-Mn particles. No evident dynamic recrystallization (DRX) takes place during warm rolling process, which is more likely attributed to the finely dispersed particle and high solid solution of Al and Mn atoms in α-Mg matrix. After annealing at 350 °C for 1 h, the warm rolled TRC sheets show fine equiaxed grains around 7.8 μm in average size. It has been shown that the present TRC alloy sheet has superior tensile strength and comparative elongation compared to commercial ingot cast (IC) one, suggesting the possibility of the development of wrought magnesium alloy sheets by twin roll strip casting processing. The microstructural evolution during warm rolling and subsequent annealing as well as the resulting tensile properties were analyzed and discussed.     

Effects of magnesium and copper additions on tensile properties of Al-Si-Cr die casting alloy under as-cast and T5 conditions

Aluminum high pressure die casting(HPDC) technology has evolved in the past decades, enabling stronger and larger one-piece casting with significant part consolidation. It also offers a higher design freedom for more mass-efficient thin-walled body structures. For body structures that require excellent ductility and fracture toughness to be joined with steel sheet via self-piercing riveting(for instance, shock towers and hinge pillars, etc.),a costly T7 heat treatment comprising a solution heat ...     

Effects of Gd Addition on the Microstructure and Tensile Properties of Mg-4Al-5RE Alloy Produced by Three Different Casting Methods

This work deals with the effect of 0.67 wt％ Gd addition on the microstructure and tensile properties of Mg-4Al-5RE (where RE represents LaCe mischmetal) alloy produced by sand casting (SC),permanent mold casting (PMC),and high-pressure die casting (HPDC).The results show that Gd addition could refine the grains,but its efficiency decreases by increasing the cooling rate due to the shifting from SC to PMC and finally to the HPDC method.Meanwhile,the acicular Al11RE3 phase is modified into the short-rod or granular-like shape under the three casting conditions.Such refined and modified micro-structures are due to the Al2(Gd,RE) phases,which act as the nucleation sites in both the α-Mg matrix and Al11RE3 phase.Also,the weakening grain refinement effect in the increased cooling rates can be attributed to the narrow constitutional undercooling zone.After Gd addition,the 0.2％ proof strength of the SC and PMC alloys increases by about 16.9％ and 12.7％,respectively,while in the HPDC alloy,it decreases by about 5.9％.The main factor in the strength increment of the SC and PMC alloys is the grain boundary strengthening due to grain refinement which is proved by modeling the related mechanisms,whereas weak secondary phases and grain boundary strengthening mechanisms in the HPDC alloy lead to strength reduction.After Gd addition,the elongation to failure of the SC,PMC,and HPDC alloys is significantly enhanced by about 34.8％,20.2％,and 12.3％,respectively,due to the crack resistance nature of the modified short-rod/granular Al11(RE,Gd)3 phase compared to the acicular one.     

消失模壳型铸造A356铸态和T6态铝合金的组织、性能及拉伸断口(英文)

对采用消失模壳型铸造制备的A356铝合金在铸态和T6热处理态下的微观组织、拉伸性能以及拉伸断口进行了研究,并与消失模铸造A356铝合金进行了对比分析。结果表明:消失模壳型铸造A356铝合金组织主要有α(Al)初生相、共晶硅相以及Mg2Si相组成。经过T6热处理后,共晶硅形貌更加球化,均匀地分布于晶界处;且共晶硅粒子的平均长度、宽度和长宽比都比铸态条件下的小。与消失模铸造相比,组织中的初生相和共晶硅相都明显细化。经T6处理后,消失模壳型铸造A356合金的力学性能得到明显提高,其中抗拉强度、延伸率和布氏硬度分别达到260.53MPa、6.15%和86.0,其与消失模铸造相比具有明显优势。此外,消失模壳型铸造A356铝合金拉伸断口为具有准解理面和韧窝形貌的混合断口,最终表现为穿晶断裂模式。而消失模铸造A356铝合金拉伸断口为明显的脆性断口。     

Effect of mold oscillation on the metallurgical characterization and mechanical properties of A319 aluminum alloy casting

Effect of mold oscillation on metallurgical characterization and mechanical properties of the A319 alloy was investigated. Experimental results show that the microstructure of A319 alloy was significantly refined regarding α-Al grain refinement along with improved silicon particle morphology due to mold oscillations. Mechanical properties of casting such as tensile strength, yield strength, percentage elongation and micro-hardness improved by 39.05, 28.05%, 2.67 times and 27.02% respectively as compared to that of stationary casting. This investigation is an attempt to study the effect of mold frequency on mechanical and metallurgical properties of aluminum alloys.     

Gating system optimization of high pressure die casting thin-wall AlSi10MnMg longitudinal loadbearing beam based on numerical simulation

High pressure die casting(HPDC) is a kind of near net shape manufacturing method. However, air entrapment in HPDC parts has serious effects upon the casting quality. In order to reduce the air entrapment defects in a AlSi10 MnMg alloy thin-wall longitudinal load-bearing beam produced by HPDC, different gating systems were designed and simulated by software Flow-3D to evaluate the entrapped air. Simulation results showed that when the beam is produced by the original designed gating system with a middle ingate, there exist obvious air entrapments in the critical area; the volume of air entrapment was reduced by replacing the middle ingate to an overflow well, and the filling of molten metal became more stable. When the middle ingate was removed for further improvement, the volume of air entrapment was decreased drastically. The parts with glossy surface and good microstructure have been successfully produced by using the final optimized gating system based on simulation results.     

Semi-solid squeeze casting process of a ZL109 alloy

The structure evolution of the ZL109 alloy in the process of semi-solid squeeze casting and the mechanical properties of the components were investigated. The results show that (1) the eutectic silicon phase in original billets is refined in the low super-heat casting process; (2) the eutectic structure in billets starts to fuse and the crystals of the eutectic silicon phase are refined further and sphericized in the remelting process of billets; (3) in the semi-solid ,squeeze casting process, the sphericity of the α phase and the refining of the silicon phase occur, owing to the friction between solid and liquid; (4) in the process of heat treatment, the eutectic α phase aggregates with the primary α phase and the eutectic silicon pieces aggregate together. The elongation of the semi-solid component after heat treatment rises to 1.42%.     

离心铸造过共晶Al-Si合金自生梯度复合材料及其阻尼性能

通过改变离心铸造的转速 ,获得了内层有较多初晶Si,其余部分为共晶组织或初晶Si由外向内偏析的Al 16 %Si合金自生梯度复合材料。分析了复合材料的形成过程 ,考察了复合材料的组织 ,研究了复合材料各层的阻尼性能。结果表明 :Al 16 %Si合金自生梯度复合材料内层内耗是中、外层的 1.4倍 ,为充分发挥此材料的阻尼性能 ,应在频率高于 16 0Hz使用     

Centrifugal casting processes of manufacturing <Emphasis Type="Italic">in situ</Emphasis> functionally gradient composite materials of Al-19Si-5Mg alloy

Cylindrical components of in situ functionally gradient composite materials of Al-19Si-5Mg alloy were manufactured by centrifugal casting. Microstructure characteristics of the manufactured components were observed and the effects of the used process factors on these characteristics were analyzed. The results of observations shows that, in thickness, the components possess microstructures accumulating lots of Mg₂Si particles and a portion of primary silicon particles in the inner layer, a little Mg₂Si and primary silicon particles in the outer layer, and without any Mg₂Si and primary silicon particle in the middle layer. The results of the analysis indicate that the rotation rate of centrifugal casting, mould temperature, and melt pouring temperature have evidently affected the accumulation of the second phase particles. Also, the higher the centrifugal rotation rate, mould temperature, and melt pouring temperature are, the more evident in the inner layer the degree of accumulation of Mg₂Si and primary silicon particles is.     

Interfacial heat transfer behavior at metal/die in finger-plated casting during high pressure die casting process

Heat transfer at the metal-die interface has a great influence on the solidification process and casting structure. As thin-wall components are extensively produced by high pressure die casting process(HPDC), the B390 alloy finger-plate casting was cast against an H13 steel die on a cold-chamber HPDC machine. The interfacial heat transfer behavior at different positions of the die was carefully studied using an inverse approach based on the temperature measurements inside the die. Furthermore, the filling process and the solidification rate in different finger-plates were also given to explain the distribution of interfacial heat flux(q) and interfacial heat transfer coefficient(h). Measurement results at the side of sprue indicates that qmax and hmax could reach 9.2 MW·m~(-2) and 64.3 kW ·m~(-2)·K~(-1), respectively. The simulation of melt flow in the die reveals that the thinnest(T_1) finger plate could accelerate the melt flow from 50 m·s~(-1) to 110 m·s~(-1). Due to this high velocity, the interfacial heat flux at the end of T_1 could firstly reach a highest value 7.92 MW·m~(-2) among the ends of T_n(n=2,3,4,5). In addition, the q_(max) and h_(max) values of T_2, T_4 and T_5 finger-plates increase with the increasing thickness of the finger plate. Finally, at the rapid decreasing stage of interfacial heat transfer coefficient(h), the decreasing rate of h has an exponential relationship with the increasing rate of solid fraction(f).     

Al-35La铸态合金的显微组织和力学性能

采用真空熔炼方法,在不同铸型(金属型、石墨型和砂型)中制备了Al-35La合金试样,研究了其组织形貌和力学性能及组织的形成原因。结果表明,Al-35La合金在不同铸型中的凝固组织均是周期性双相枝晶组织;不同铸型中试样的硬度和相对压缩率相差不大;合金的抗压强度较高且具有10%左右的相对压缩率,这与合金组织中Al11La3枝晶不连续分布,从而使组织细化的特征相一致。     

影响消失模铸造Al-Si-Cu合金薄壁铸件质量的显著性工艺参数

通过控制消失模铸造工艺参数可以制备出无缺陷的形状复杂的铸件产品。对Al-Si-Cu合金消失模铸造进行研究,考察浇注温度、涂料黏度、振动时间、型砂粒径以及它们之间的交互作用对铸件表面质量、孔隙率和共晶硅间距的影响。采用两水平全因子实验设计方法考察影响铸件性能的显著性影响工艺参数。结果表明,浇注温度和振动时间对铸件共晶硅间距和孔隙率的影响最明显。在细型砂模和较高的浇注温度下,铸件的表面质量几乎保持稳定不变,而在粗型砂模下铸件的表面质量较低。涂料黏度对铸件性能没有显著影响。     

Effects of temperature on fracture behavior of Al-based in-situ composites reinforced with Mg2Si and Si particles fabricated by centrifugal casting

An aluminum-based in-situ composites reinforced with Mg₂Si and Si particles were produced by centrifugal casting Al–20Si–5Mg alloy. The microstructure of the composites was examined, and the effects of temperature on fracture behavior of the composite were investigated. The results show that the average fraction of primary Si and Mg₂Si particles in the composites is as high as 38%, and ultimate tensile strengths (UTS) of the composites first increase then decrease with the increase of test temperature. Microstructures of broken specimens show that both the particle fracture and the interface debonding affect the fracture behavior of the composites, and the interface debonding becomes the dominant fracture mechanism with increasing test temperature. Comparative results indicate that rich particles in the composites and excellent interface strength play great roles in enhancing tensile property by preventing the movement of dislocations.