Thin-walled and large-sized magnesium alloy die castings for passenger car cockpit:Application,materials,and manufacture

In order to effectively reduce energy consumption and increase range mile,new energy vehicles represented by Tesla have greatly aroused the application of integrated magnesium(Mg)alloy die casting technology in automobiles.Previously,the application of Mg alloys in automobiles,especially in automotive cockpit components,is quite extensive,while it has almost disappeared for a period of time due to its relatively high cost,causing a certain degree of information loss in the application technology of Mg alloy parts in automobiles.The rapid development of automotive technology has led to a higher requirement for the automotive components compared with those traditional one.Therefore,whatever the components themselves,or the Mg alloy materials and die casting process have to face an increasing challenge,needing to be upgraded.In addition,owing to its high integration characteristics,the application of Mg alloy die casting technology in large-sized and thin-walled automotive parts has inherent advantages and needs to be expanded urgently.Indeed,it necessitates exploring advance Mg alloys and new product structures and optimizing die casting processes.This article summarizes and analyzes the development status of thin-walled and large-sized die casting Mg alloy parts in passenger car cockpit and corresponding material selection methods,die casting processes as well as mold design techniques.Furthermore,this work will aid researchers in establishing a comprehensive understanding of the manufacture of thin-walled and large-sized die casting Mg alloy parts in automobile cockpit.It will also assist them in developing new Mg alloys with improved comprehensive performance and new processes to meet the high requirements for die casting automotive components.

Compression properties of cost-efficient porous expanded clay reinforced AA7075 syntactic foams fabricated by industrial-oriented die casting technology

In today’s manufacturing industries,hard competition between rival firms makes it compulsory for researchers to design lighter and cheaper machine components due to the megatrends of cost-effectiveness and anti-pollution.At this point,aluminum syntactic foams(ASFs)are new-generation engineering composites and come into the upfront as a problem-solver.Owing to their features like low density,sufficient elongation,and perfect energy absorption ability,these advanced foams have been considerably seductive for many industrial sectors nowadays.In this study,an industrial-oriented automatic die casting technology was used for the first time to manufacture the combination of AA7075/porous expanded clay(PEC).Micro evaluations(optical and FESEM)reveal that there is a homogenous particle distribution in the foam samples,and inspections are compatible with the other ASF studies.Additionally,T6 aging heat treatment was operated on one half of the produced foams to explore the probable impact of aging on the compressive responses.Attained results show that PEC particles can be an alternative to expensive hollow spheres used in the previous works.Besides,a favorable relationship is ascertained between the aging treatment and mechanical properties such as compression strength and plateau strength.

Characteristics and distribution of microstructures in high pressure die cast alloys with X-ray microtomography:A review

Al and Mg alloy high pressure die castings(HPDC)are increasingly used in automotive industries.The microstructures in the castings have decisive effect on the casting mechanical properties,in which the microstructure characteristics are fundamental for the investigation of the microstructure-property relation.During the past decade,the microstructure characteristics of HPDC Al and Mg alloys,especially micro-pores andα-Fe,have been investigated from two-dimensional(2D)to threedimensional with X-ray micro-computed tomography(μ-CT).This paper provides an overview of the current understanding regarding the 3D characteristics and formation mechanisms of microstructures in HPDC alloys,their spatial distributions,and the impact on mechanical properties.Additionally,it outlines future research directions for the formation and control of heterogeneous microstructures in HPDC alloys.

Effect of slow shot speed on externally solidified crystal,porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy

The effect of slow shot speed on externally solidified crystal(ESC),porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy was investigated by optical microscopy(OM),scanning electron microscopy(SEM)and laboratory computed tomography(CT).Results showed that the newly developed AlSi9MnMoV alloy exhibited improved mechanical properties when compared to the AlSi10MnMg alloy.The AlSi9MnMoV alloy,which was designed with trace multicomponent additions,displays a notable grain refining effect in comparison to the AlSi10MnMg alloy.Refining elements Ti,Zr,V,Nb,B promote heterogeneous nucleation and reduce the grain size of primaryα-Al.At a lower slow shot speed,the large ESCs are easier to form and gather,developing into the dendrite net and net-shrinkage.With an increase in slow shot speed,the size and number of ESCs and porosities significantly reduce.In addition,the distribution of ESCs is more dispersed and the net-shrinkage disappears.The tensile property is greatly improved by adopting a higher slow shot speed.The ultimate tensile strength is enhanced from 260.31 MPa to 290.31 MPa(increased by 11.52%),and the elongation is enhanced from 3.72%to 6.34%(increased by 70.52%).

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 treatment at elevated temperatures(450℃-500℃)followed by an over-ageing heat treatment is needed to optimize microstructure for meeting product requirement.To enable cost-efficient mass production of HPDC body structures,it is important to eliminate the expensive T7 heat treatment without sacrificing mechanical properties.Optimizing die cast alloy chemistry is a potential solution to improve fracture toughness and ductility of the HPDC components.The present study intends to tailor the Mg and Cu additions for a new Al-Si-Cr type die casting alloy(registered as A379 with The Aluminum Association,USA)to achieve the desired tensile properties without using T7 heat treatment.It was found that Cu addition should be avoided,as it is not effective in enhancing strength while degrades tensile ductility.Mg addition is very effective in improving strength and has minor impact on tensile ductility.The investigated Al-Si-Cr alloy with a nominal composition of Al-8.5wt.%Si-0.3wt.%Cr-0.2wt.%Fe shows comparable tensile properties with the T7 treated AlSi10MnMg alloy which is currently used for manufacturing shock towers and hinge pillars.

Low cycle fatigue behavior of T4-treated Al-Zn-Mg-Cu alloys prepared by squeeze casting and gravity die casting

Gravity die casting(GC) and squeeze casting(SC) T4-treated Al-7.0Zn-2.5Mg-2.1Cu alloys were employed to investigate the microstructures,mechanical properties and low cycle fatigue(LCF) behavior.The results show that mechanical properties of SC specimens are significantly better than those of GC specimens due to less cast defects and smaller secondary dendrite arm spacing(SDAS).Excellent fatigue properties are obtained for the SC alloy compared with the GC alloy.GC and SC alloys both exhibit cyclic stabilization at low total strain amplitudes(less than 0.4%) and cyclic hardening at higher total strain amplitudes.The degree of cyclic hardening of SC samples is greater than that of GC samples.Fatigue cracks of GC samples dominantly initiate from shrinkage porosities and are easy to propagate along them,while the crack initiation sites for SC samples are slip bands,eutectic phases and inclusions at or near the free surface.

Determination of wax pattern die profile for investment casting of turbine blades

In order to conform to dimensional tolerances, an efficient numerical method, displacement iterative compensation method, based on finite element methodology （FEM） was presented for the wax pattern die profile design of turbine blades. Casting shrinkages at different positions of the blade which was considered nonlinear thermo-mechanical casting deformations were calculated. Based on the displacement iterative compensation method proposed, the optimized wax pattern die profile can be established. For a A356 alloy blade, substantial reduction in dimensional and shape tolerances was achieved with the developed die shape optimization system. Numerical simulation result obtained by the proposed method shows a good agreement with the result measured experimentally. After four times iterations, compared with the CAD model of turbine blade, the total form error decreases to 0.001 978 mm from the orevious 0.515 815 mm.

Vacuum assisted high-pressure die casting of AZ91D magnesium alloy at different slow shot speeds

The effects of vacuum assistance on the microstructure and mechanical properties of high-pressure die cast AZ91 D alloy at different slow shot speeds were evaluated. Plate-shaped castings of AZ91 D alloy were carried out on a TOYO BD-350V5 cold chamber die casting machine incorporated with a self-improved TOYO vacuum system. It was found that the vacuum pressure in the die cavity at the beginning of mold filling increases with the increase of slow shot speed, following a cubic polynomial curve, resulting in a decline in the porosity-reduction ability of vacuum assistance with the increase of slow shot speed. The externally solidified crystal（ESC） contents in conventional and vacuum die castings behave similar against the slow shot speed. The tensile properties of vacuum die castings were strongly influenced by the ESC content at relative low slow shot speeds. With the increase of slow shot speed, the influence of the gas porosity level in vacuum die castings would get prominent.

基于ProCAST的一模多腔YL112铝合金压铸件数值模拟及工艺优化

针对YL112压铸铝合金一模多铸产品的组织性能均一性需求,采用ProCAST软件对典型一模多铸工艺进行模拟,比较了两种不同充型顺序的压铸方案。结果表明:基于顺序凝固一模多腔压铸件由于充型与凝固过程的温度场分布不均,导致近浇口端铸件出现明显缩松缩孔缺陷,造成铸件性能均一性差。后续采用等流程浇注系统,实现一模多腔铸件同时充型凝固过程,改善了铸件温度场分布,减少了工艺缺陷。经过实际生产验证,获得了组织性能均一性好的压铸件。

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.

Temperature change and stress distribution analysis of die surface in Al-alloy die casting process and experimental study on die heat check

The temperature change of the die surface in practical aluminum alloy die casting process was analyzed,and a 2D model was formulated on the basis of a deep concave round cavity without sliding core to analyze thestress distributions along the die surface in detail. Equipment was designed to test the thermal state of the die steelin different thermal loading conditions. The results of stress analysis showed that, the value of thermal stress (maximum1.5 GPa) caused in the die filling and die spraying stages was larger than the mechanical stress (maximum 85 MPa)caused in the die locking stage. The results of the thermal check experiment showed that there were three stages ofdie dissolving, and that the stress distribution shown by the samples' cracking routine was close to the die surfacestress analysis.

Finite element analysis for die casting parameters in high-pressure die casting process

The gating system and the overflow system were designed according to the casting structure during high pressure die casting(HPDC) process. The simulation was carried out by ProCAST software to visualize the injection chamber pre-crystallization and the flow of molten metal. The main work is to research four die casting process parameters, i.e. injection temperature, low-pressure velocity, high-and low-pressure velocity’s switching position, and high-pressure velocity. Experimental results show that the higher injection temperature and lowpressure velocity can mitigate the pre-crystallization of the injection chamber. However, when the low-pressure velocity exceeds 0.2 m·s-1, the air entrapment in the chamber occurs. Besides, when the high-pressure velocity is greater than 2.5 m·s-1, the overflow channel at the final filling position is covered by the liquid metal too early. Finally, the injection temperature of 650 °C, the low-pressure velocity of 0.2 m·s-1, the high-and low-pressure velocity’s switching position of 320 mm and the high-pressure velocity of 2 m·s-1 are obtained as the optimal parameters by the software simulation, which has been verified by actual production.

Determination of interfacial heat transfer coefficient and its application in high pressure die casting process

In this paper,the research progress of the interfacial heat transfer in high pressure die casting(HPDC)is reviewed.Results including determination of the interfacial heat transfer coefficient(IHTC),influence of casting thickness,process parameters and casting alloys on the IHTC are summarized and discussed.A thermal boundary condition model was developed based on the two correlations:(a)IHTC and casting solid fraction and(b)IHTC peak value and initial die surface temperature.The boundary model was then applied during the determination of the temperature field in HPDC and excellent agreement was found.

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).

Die Casting Mold Design of the Thin-walled Aluminum Case by Computational Solidification Simulation

Recently, demand for the lightweight alloy in electric/electronic housings has been greatly increased. However, among the lightweight alloys, aluminum alloy thin-walled die casting is problematic because it is quite difficult to achieve sufficient fluidity and feedability to fill the thin cavity as the wall thickness becomes less than 1mm. Therefore, in this study, thin-walled die casting of aluminum （Al-Si-Cu alloy： ALDC 12） in size of notebook computer housing and thickness of 0.8 mm was investigated by solidification simulation （MAGMA soft） and actual casting experiment （Buhler Evolution B 53D）. Three different types of gating design, finger, tangential and split type with 6 vertical runners, were simulated and the results showed that sound thin-walled die casting was possible with tangential and split type gating design because those gates allowed aluminum melt to flow into the thin cavity uniformly and split type gating system was preferable gating design comparing to tangential type gating system at the point of view of soundness of casting and distortion generated after solidification. Also, the solidification simulation agreed well with the actual die-casting and the casting showed no casting defects and distortion.

Simulation of mold filling and prediction of gas entrapment on practical high pressure die castings

Element parameters including volume filled ratio,surface dimensionless distance,and surface filled ratio for DFDM(direct finite difference method)were proposed to describe shape and location of free surfaces in casting mold filling processes.A mathematical model of the filling process was proposed specially considering the mass,momentum and heat transfer in the vicinity of free surfaces.Furthermore,a method for gas entrapment was established by tracking flow of entrapped gas.The model and method were applied to practical ADC1 high pressure die castings.The gas entrapment prediction was compared with the fraction and maximum size of porosities in the different casting parts.The comparison shows validity of the proposed model and method.The study indicates that final porosities in high pressure die castings are dependent on both gas entrapment during mold filling process and pressure transfer within solidification period.

Performance of Semi-solid Slurry Produced by Twin-screw Stirring Mixer and Rheo-diecasting Process of AZ91D Alloy

The microstructure of semi-solid slurry of AZ91D alloy, which was produced by twin-screw stirring mixer under the different parameters, was investigated.Rheoforming by cold chamber die casting process was performed thereafter. The results indicate that with decreasing of the barrel temperature of the mixer and the pouring temperature of molten Mg alloy, the solid fraction of semi-solid slurry increases and the size of non-dendritic grains becomes smaller. While the shear rate increases, the solid fraction of semi-solid slurry decreases. The tensile strength and elongation of metal rheoformed by die casting are higher by about 37% and 44% respectively than those produced by conventional liquid die casting.

LOW CYCLE FATIGUE BEHAVIOR OF AZ91HP ALLOY IN AS HIGHP RESSURE DIE CASTING

Fully reversed total strain-controlled low-cycle fatigue tests were conducted at room temperature in air to study the fatigue behavior of AZ91HP magnesium alloy in as high pressure die casting and subsequently heat treatment. All the specimens in different heat histories exhibit cyclic strain hardening in different degrees. It is difficult to distinguish the fatigue behavior of the die casting specimens from that of the solution aging specimens. The solution treated specimens show longer fatigue life at high strain amplitude and shorter fatigue life at low strain amplitude than the die casting and solution aging specimens though they have the lowest yield strength with higher strain hardening. Fatigue fracture surfaces for strain amplitude larger than 0.005 show very similar to those found by monotonic tensile tests. The SEM examination reveals that the regions of fatigue crack growth and final fracture can be characterized by quasi-cleavage mechanisms, but some shallow dimples, slip bands and secondary cracks are found on the fracture surface in the fracture crack growth areas.

Design and Verification of an Auxiliary System for High Vacuum Die Casting

Vacuum die casting is the optimal method to produce high quality aluminum alloy components.At present,there are still very few systematic studies on vacuum die casting theory and equipment design.On the basis of the existing theories of the vacuum die casting pumping and venting systems,a simplified model is established in this research.The model has an aggregate unit consisted of ＂vacuum pump ＋ buffer tank＂ and a cylindrical container（including the shot sleeve,cavity and exhaust channel）.The theoretical analysis is carried out between the cavity pressure and the pumping time under different volume models.An auxiliary system for high vacuum die casting is designed based on the above analysis.This system is composed of a vacuum control machine and a new vacuum stop valve.The machine has a human-computer control mode with ＂programmable logic controller（PLC） ＋ touch screen＂ and a real-time monitoring function of vacuum degree for buffer tank and die cavity.The vacuum stop valve with the ＂compressed gas ＋ piston rod ＋ labyrinth groove＂ structure can realize the function of whole-process vacuum venting.The new system shows great advantages on vacuuming the cavity with a much faster speed by making tests on an existing die casting mold and a 250 t die casting machine.A die cavity pressure less than 10 kPa can be reached within 0.8 s in the experiment and the porosity of castings can be greatly decreased.The systematic studies on vacuum die casting theory and equipment have a great guiding significance for high vacuum die casting,and can also be applied to other high vacuum forming in related theoretical and practical research.

Microstructural characteristics of near-liquidus cast AZ91D alloy during semi-solid die casting

Near-liquidus cast ingot was reheated to semi-solid firstly, and then a bracket of motor was prepared by die casting the semi-solid ingot into mould. The microstructural characteristics of AZ91D alloy in these processes were investigated. In the process of near-liquidus casting, primary α-Mg grains tend to be rosette-like because of the increase of plentiful quasi-solid atom clusters in molten alloy with the decrease of pouring temperature. These rosette-like a-Mg grains in ingots fabricated by near-liquidus casting are fused off and refined into near-globular structure owing to the solute diffusion mechanism and the minimum surface energy mechanism during reheating. After semi-solid die-casting, a-Mg grains, located in biscuit, impact and connect with each other; α-Mg grains, located in inner gate, congregate together; while α-Mg grains, located in component, distribute uniformly and become into globularity or strip. Because the inner gate limits the flowing of semi-solid slurry, and the pressure acted on the semi-solid slurry decreases gradually along the filling direction of semi-solid slurry in Cavity, microstructural segregation of unmelted a-Mg grains appears along this direction. Shrinkage holes in casting are caused by two different reasons. For biscuit, the shrinkage holes are caused by the blocked access of feeding liquid to the shrinkage zone for the agglomerated unmelted α-Mg grains. For component, the shrinkage holes are caused by the lack of feeding of liquid alloy.