A review of magnesium die-castings for closure applications

Vehicle mass reduction in the automotive industry has become an industry-wide objective.Increasing fuel efficiency and greenhouse gas emission targets for engine-powered vehicles,and ambitions for extended range electric vehicles have motivated these reductions in vehicle mass.Mass reduction opportunities in structural automotive applications are increasingly realized through lightweight alloy castings,such as magnesium,primarily due to the ease of component substitution.The traditional benefits of magnesium die-castings including lightweighting and associated compounded mass savings,excellent strength-to-weight ratio,part consolidation,near net-shape forming,dimensional repeatability,and integration of additional components can be realized in closure applications.One recent example is the application of a magnesium die-casting for the structural inner of the liftgate in the 2017 Chrysler Pacifica,replacing nine parts in the previous generation and resulting in a liftgate assembly weight reduction of nearly 50%.The work presented here reviews past and current developments of magnesium die-castings in closure applications and discusses the benefits and challenges of magnesium alloys for these applications,including casting design,corrosion and fastening strategies,and the manufacturing design and assembly methodologies.

Influence of introducing Zr,Ti,Nb and Ce elements on externally solidified crystals and mechanical properties of high-pressure die-casting Al–Si alloy

High pressure die casting(HPDC)AlSi10Mn Mg alloy castings are widely used in the automobile industry.Mg can optimize the mechanical properties of castings through heat treatment,while the release of thermal stress arouses the deformation of large integrated die-castings.Herein,the development of non-heat treatment Al alloys is becoming the hot topic.In addition,HPDC contains externally solidified crystals(ESCs),which are detrimental to the mechanical properties of castings.To achieve high strength and toughness of non-heat treatment die-casting Al-Si alloy,we used AlSi9Mn alloy as matrix with the introduction of Zr,Ti,Nb,and Ce.Their influences on ESCs and mechanical properties were systematically investigated through three-dimensional reconstruction and thermodynamic simulation.Our results reveal that the addition of Ti increased ESCs'size and porosity,while the introduction of Nb refined ESCs and decreased porosity.Meanwhile,large-sized Al_3(Zr,Ti)phases formed and degraded the mechanical properties.Subsequent introduction of Ce resulted in the poisoning effect and reduced mechanical properties.

Assessing efficacy of standard impregnation techniques on die-cast aluminum alloys using X-ray micro-CT

Utilizing lightweight Al alloys in various industrial applications requires achieving precise pressure tightness and leak requirements.Vacuum pressure impregnation(VPI)with thermosetting polymers is commonly used to address leakage defects in die-cast Al alloys.In this study,the efficacy of the VPI technique in sealing alloy parts was investigated using a combination of nondestructive micro X-ray computed tomography(micro XCT)and a standard leak test.The results demonstrate that the commonly used water leak test is insufficient for determining the sealing performance.Instead,micro XCT shows distinct advantages by enabling more comprehensive analysis.It reveals the presence of a low atomic number impregnates sealant within casting defects,which has low grey contrast and allows for visualizing primary leakage paths in 3D.The effective atomic number of impregnated resin is 6.75 and that of Al alloy is 13.69 by dual-energy X-ray CT.This research findings will contribute to enhancing the standard VPI process parameters and the properties of impregnating sealants to improve quality assurance for impregnation in industrial metals.

Effects of on-line solution and off-line heat treatment on microstructure and hardness of die-cast AZ91D alloy

The effects of on-line solution, off-line solution and aging heat treatment on the microstructure and hardness of the die-cast AZ91D alloys were investigated. Brinell hardness of die-cast AZ91D alloy increases through on-line solution and off-line aging treatment but decreases after off-line solution treatment. By X-ray diffractometry, optical microscopy, differential thermal analysis, scanning electron microscopy and X-ray energy dispersive spectroscopy, it is found that the microstructures of the die-cast AZ91D magnesium alloy before and after on-line solution and off-line aging are similar, consisting of α-Mg and β-Al12Mg17. The precipitation of Al element is prevented by on-line solution so that the effect of solid solution strengthening is enhanced. The β-Al12Mg17 phases precipitate from supersaturated Mg solid solution after off-line aging treatment, and lead to microstructure refinement of AZ91D alloy, so the effect of precipitation hardening is enhanced. The β-Al12Mg17 phases dissolve in the substructure after off-line solution treatment, which leads to that the grain boundary strengthening phase is reduced significantly and the hardness of die cast AZ91D is reduced.

Study on Key Joining Technology and Test Method of Steel/Al Hybrid Structure Body-in-White

Green and low carbon promote the application and development of light-weight materials in body-in-white. Large-scale die-casting Al alloy (DCAA) and high-strength thermo-formed steel sheet (TFSS) have put forward higher requirements for the application of joining technology of high-strength steel/Al dissimilar materials. Taking the new die-casting Al alloy body as an example, this paper systematically studies the progress of the latest joining methods of steel/Al dissimilar material with combination of two-layer plate and three-layer plate. By analyzing the joining technologies such as FSPR, RES, FDS and SPR, the technology and process characteristics of steel/Al dissimilar material joining are studied, and the joining technical feasibility and realization means of different material combination of the body are analyzed. The conditions of material combination, material thickness, material strength, flange height, preformed holes and joint spacing for achieving high-quality joining are given. The FSPR joining technology is developed and tested in order to meet with the joining of parts with DCAA and TFSS, especially for the joining of three-layer plates with them. It finds the method and technical basis for the realization of high quality joining of dissimilar materials, provides the early conditions for the application of large DCAA and TFSS parts in body-in-white, and meets the design requirements of new energy body. .

Microstructure and mechanical properties of Mg-6Gd-3Y-0.5Zr alloy processed by high-vacuum die-casting

GW63K （Mg-6Gd-3Y-0.5Zr） magnesium alloys were prepared successfully by high-vacuum die-casting. Effects of fast shot speed and vacuum level on the grain size and mechanical properties of this alloy were studied. Microstructure of the alloys was analyzed by SEM, EDX and optical microscope （OM）. The effect of heat treatment on high vacuum die-casting （HVDC） GW63K alloy was also studied. The results indicate that with the increase of fast velocity, the tensile yield strength hardly changes, but the elongation first increases, then decreases. The optimum heat treatment process is solution treatment at 748 K for 2 h and aging at 473 K for 80 h. Under this condition, GW63K magnesium alloy exhibits a maximum tensile strength and elongation of 308 MPa and 9.45%. There is significant correlation between ductility and the presence of external solidified cells （ESCs）. The as-cast GW63K alloy consists ofα-Mg and Mg24（Gd,Y）5 particles. After heat treatment, Gd and Y atoms dissolve intoα-Mg matrix.

Development of vacuum die-casting process

The vacuum die-casting process,started 25 years ago in Japan,has been widely applied.This technology contributes very much to improvement of castings quality.The main factor causing the defects of die castings is the trapped air in the mold cavity,while the key technology of vacuum die-casting process is to avoid the trapped air effectively by evacuating the cavity before casting.At the same time,due to the shot speed and the casting pressure reduced in half,the service life of the die is prolonged and the productivity is enhanced,as well.Vacuum die-casting process is of great signif icance in improving the die castings quality and making up the shortcomings of super-high-speed shot casting.

High Cycle Fatigue Properties of Die-Cast Magnesium Alloy AZ91D with Addition of Different Concentrations of Cerium

The effect of addition of different concentrations of Ce on high-cycle fatigue behavior of die-cast magnesium alloy AZ91D was investigated. Mechanical fatigue tests were conducted at the stress ratio of R = 0.1, and fatigue strength was evaluated using up-and-down loading method. The results show that the grain size of AZ91D alloy is remarkably refined, and the amount of porosity decreases and evenly distributes with the addition of Ce. The fatigue strength of AZ91D alloy at room temperature increases from 96.7 up to 116.3 MPa （ 1% Ce） and 105.5 MPa （2 % Ce）, respectively, at the number of cycles to failure, Nf = 1 × 10^7. The fatigue crack of AZ91D alloy initiates at porosities and inclusions, and propagates along grain boundaries. The fatigue striations on fractured surface appear with Ce addition. The fatigue fracture surface of test specimens shows mixed-fracture characteristics of quasi-cleavage and dimple.

Corrosion performance of high pressure die-cast Al-6Si-3Ni and Al-6Si-3Ni-2Cu alloys in aqueous NaCl solution

The corrosion performance of high pressure die-cast Al？6Si？3Ni （SN63） and Al-6Si-3Ni-2Cu （SNC632） alloys in 3.5%（mass fraction） NaCl solution was investigated. X-ray diffraction （XRD） and microstructural studies revealed the presence of singlephase Si and binary Al3Ni/Al3Ni2 phases along the grain boundary. Besides, the single Cu phase was also identified at the grainboundaries of the SNC632 alloy. Electrochemical corrosion results revealed that, the SNC632 alloy exhibited nobler shift incorrosion potential （φcorr）, lower corrosion current density （Jcorr） and higher corrosion resistance compared to the SN63 alloy.Equivalent circuit curve fitting analysis of electrochemical impedance spectroscopy （EIS） results revealed the existence of twointerfaces between the electrolyte and substrate. The surface layer and charge transfer resistance （Rct） of the SNC632 alloy was higherthan that of the SN63 alloy. Immersion corrosion test results also confirmed the lower corrosion rate of the SNC632 alloy andsubstantiated the electrochemical corrosion results. Cu addition improved the corrosion resistance, which was mainly attributed to theabsence of secondary Cu containing intermetallic phases in the SNC632 alloy and Cu presented as single phase.

Simulation of α-Al grain formation in high vacuum die-casting Al-Si-Mg alloys with multi-component quantitative cellular automaton method

Al-Si-Mg alloys are the most commonly used material in high vacuum die-casting(HVDC),in which the morphology and distribution ofα-Al grains have important effect on mechanical properties.A multi-component quantitative cellular automaton(CA)model was developed to simulate the microstructure and microsegregation of HVDC Al-Si-Mg alloys with different Si contents(7%and 10%)and cooling rates during solidification.The grain number and average grain size with electron backscatter diffraction(EBSD)analysis were used to verify the simulation.The relationship between grain size and nucleation order as well as nuclei density was investigated and discussed.It is found that the growth of grains will be restrained in the location with higher nuclei density.The influence of composition and cooling rate on the solute transport reveals that for AlSi7Mg0.3 alloy the concentration of solute Mg in liquid is higher at the beginning of eutectic solidification.The comparison between simulation and experiment results shows that externally solidified crystals(ESCs)have a significant effect for samples with high cooling rate and narrow solidification interval.

Low-cycle fatigue behavior of permanent mold cast and die-cast Al-Si-Cu-Mg alloys

Fatigue failure is one of the main failure forms of Al-Si-Cu-Mg aluminum alloys. To feature their mechanical aspect of fatigue behavior, the low-cycle fatigue behavior of permanent mold cast and die-cast AI-Si- Cu-Mg alloys at room temperature was investigated. The experimental results show that both permanent mold cast and die-cast AI-Si-Cu-Mg alloys mainly exhibit cyclic strain hardening. At the same total strain amplitude, the diecast AI-Si-Cu-Mg alloy shows higher cyclic deformation resistance and longer fatigue life than does the permanent mold cast AI-Si-Cu-Mg alloy. The relationship between both elastic and plastic strain amplitudes with reversals to failure shows a monotonic linear behavior, and can be described by the Basquin and Coffin-Manson equations, respectively.

Mold Filling and Prevention of Gas Entrapment in High-pressure Die-casting

This paper presents some results of direct observation of mold filling in a specially designed die-casting by X-ray diffraction, including comparison with numerical simulation. Based on such work the authors discuss how to prevent gas entrapment and propose new methods.

Thin-Wall Aluminum Die-Casting Technology for Development of Notebook Computer Housing

Silicon-based aluminum casting alloys are known to be one of the most widely used alloy systems mainly due to their superior casting characteristics and unique combination of mechanical and physical properties. However,manufacturing of thin-walled aluminum die-casting components,less than 1.0 mm in thickness,is generally known to be very difficult task to achieve aluminum casting alloys with high fluidity.Therefore,in this study,the optimal die-casting conditions for producing 297 mm×210 mm×0.7 mm thin-walled aluminum component was examined experimentally by using 2 different gating systems,tangential and split type,and vent design.Furthermore,computational solidification simulation was also conducted.The results showed that split type gating system was preferable gating design than tangential type gating system at the point of view of soundness of casting and distortion generated after solidification.It was also found that proper vent design was one of the most important factors for producing thin-wall casting components because it was important for the fulfillment of the thin-wall cavity and the minimization of the casting distortion.

Opportunities and challenges of Chinese die-casting market

The present status and perspectives of Chinese die-casting market were commented. In 2003, the total output of die castings in the whole country was 708000 tons, in which the outputs of Al-alloy, Zn-alloy, Mg-alloy, Cu-alloy die castings were 474600 tons, 222000 tons, 5800 tons, 5600 tons, respectively, each accounted for 67%, 31.35%, 0.85%, 0.8% of the total. The annual sale volume of die-casting machines was approximately 1800. And the gross output value of dies approached RMB 38 billion, in which die-casting dies accounted for about 10%. In the die-casting industry of the entire country, the foreign capital enterprises, public-run enterprises, township and village enterprises, private enterprises accounted for over 80% of the total die-casting enterprises. Super huge die-casting groups are forming.

Development and Application of Die-Casting High Speed Steel Rolls

Due to its high hardness,good red hardness and excellent wear resistance at high temperature,high speed steel(HSS)is fit for the roll manufacture.In order to overcome the segregation of centrifugal casting of HSS roll,die-cast processes were developed and its effects on the properties of the HSS roll were investigated.It was found that pressure,pressing time and speed are three important factors affecting shrinkage cavity.For pouring temperature of 1 400-1 450 ℃,pressure of 150-160 MPa,pressing time of 120-150 sand pressing speed of 14-16mm/s,a compact HSS roll was obtained,which has no segregation and small working allowance.In the high speed wire rod rolling mill,service life of the HSS roll is 5to 8times longer than that of high nickel chromium infinite chilled cast iron roll.

Code generation and recognition using a modified ejection system in die-casting process

A code-generation and recognition technology that uses a modified ejection system in the diecasting process is presented.To achieve the highest level of quality management,the first requirement in the manufacturing process is to establish a product management system according to the specific product unit.Thus,a method to individually identify each product,such as a barcode or QR code,is required during the production process.Products manufactured in the die-casting process always have ejector pin(EP)marks.Herein,an ejection system was modified to generate a unique code using EP marks.This ejection system has two features:an EP with a modified head to show the direction of rotation,and a function to dependently rotate EPs(five or six EPs)with a constant angle.The EPs are numbered according to the rotation angle.Thus,the EP marks can be viewed as a five-or six-digit code.A program was also developed to individually identify the products by automatically detecting and reading the EPs using deep learning-based object detection and classification technology.

Two semi-solid die-casting production lines of Xuzhou Die- casting Technology Co., Ltd. officially put into operation

The two production lines for the first phase of the semi-solid die-casting high-end parts project were put into production in this October, and can monthly produce more than 30 thousand die casting parts.

An Industrial Perspective on Magnesium Alloy Wheels: A Process and Material Design

Light weights wheels improve vehicle performance with respect to road handling, cornering as well providing fuel economy and reduced greenhouse gas emissions. Aluminum wheels are currently used in many models and are produced usually by low pressure assisted gravity casting. Important property requirements are fatigue strength, pressure tightness, tensile strength, impact resistance, and corrosion resistance. Many attempts have been made to convert aluminum road wheels to magnesium. Race cars and some of the high end models (Porsche, Ferrari, etc.) have used magnesium wheels. These wheels have been gravity cast or forged. Viable corrosion protection systems have been developed and magnesium wheels have been used with success on these models. To use magnesium on more modest models is a challenge due to cost issues. Higher productivity casting processes or more cost effective coating systems need to be utilized. The project consists of selecting magnesium alloys for road wheels, examining the possible cost effective casting processes and corrosion protection systems, evaluating the cost per one wheel and comparing it to aluminum wheel costs. The wheels will also be compared with respect to fatigue and impact properties, pressure tightness, and corrosion.

Grain Size Control of Semisolid A356 Alloy Manufactured by Electromagnetic Stirring

To investigate the possibility of substituting the mechanical stirring system with electromagnetic stirring (EMS) system for aluminum rheo die-casting, the EMS under the different stirring cooling conditions was carried out. It was found that in the early period of solidification, the dendrite breakages led to a fine primary phase. When dendrites grew coarsely, the effect of ripening on grain size overwhelmed that of dendrite breakage. It was also found that the high cooling rate favored large nucleation rate, and led to a fine primary phase. But high cooling rate also made the growth rate of the dendrite arm, which prevented the dendrite arm from being sheared off. Therefore there were a suitable stirring time and suitable cooling rate to obtain the best rheo die-casting structure. Qualified semisolid A356 aluminum alloy was successfully manufactured with short time EMS.

Effect of rare earth additions on microstructure and mechanical properties of AZ91 magnesium alloys

In order to meet the demands of high temperature components in automobile, the microstructure and mechanical properties of several new die-casting AZ91-rare earth (RE) magnesium alloys were studied. The alloys were characterized by optical microscopy (OM), scan electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), tensile and creep tests. The results show that Ce addition has little effect on the mechanical properties of AZ91 alloy at high temperature, while Y and Nd addition play important role in the improvement of creep resistance. New alloys containing Y or Nd with excellent high temperature performance are selected to produce cylinder head cover of high power diesel engine of Red Flag car and oil pan of Besturn car. The new magnesium alloys with RE addition for die-casting have potential to produce power-train parts, and can greatly decrease weight.