High Pressure Die Cast Aluminum Research Articles

Friction stir processing: A thermomechanical processing tool for high pressure die cast Al-alloys for vehicle light-weighting

This study uses friction stir processing (FSP) for thermomechanical processing of high-pressure die-casting (HPDC) to modify microstructure and improve mechanical properties. FSP is carried out on two different HPDC aluminum alloys: (a) general-purpose, high-iron, HPDC A380 alloy and (b) premium quality, low-iron HPDC Aural-5 alloy in thin wall, flat plate geometry. Subsequent mechanical testing shows ∼30 % and ∼65 % enhancement in yield strength and tensile ductility. In addition, FSP leads to ∼10 times improvement in fatigue life for A380 alloy and ∼70 % improvement in fracture toughness for Aural-5 alloy. These findings emphasize the capability of FSP to modify the microstructure of HPDC Al-alloys-based structural components so that they can demonstrate a good combination of strength, ductility, fracture toughness, and high fatigue properties for long-term durability and reliability.

Cyclic deformation behavior of an overaged high-pressure die-cast aluminum alloy

The aim of this study is to identify the deformation behavior of a high-pressure die-cast Silafont®-36 aluminum alloy in an overaged T7 condition in relation to the significant microstructural changes caused by the overaging heat treatment. The T7 aluminum alloy exhibited a distinctive composite-like microstructure, consisting of coarser α-Al grains and larger spherical Si particles embedded in the matrix, in contrast to its as-cast and T4 counterparts. The softer α-Al matrix of the T7 alloy as revealed by the nanohardness and microhardness led to improved ductility and longer strain-controlled fatigue life at higher strain amplitudes, despite the lower strength. Cyclic stabilization was observed to be a salient feature of the T7 alloy, stemming from the equilibrium between cyclic hardening and cyclic softening. Strain-energy density-based model, by incorporating a material parameter called ‘intrinsic fatigue toughness’, could be used to predict the fatigue life of the alloy.

Evaluating the joinability of thin-walled high pressure die cast aluminium for automotive structures using self-piercing rivets

This paper is the first to report successful application of self-pierce riveting (SPR) in thin-walled high pressure die cast (HPDC) aluminium for use in automotive applications. HPDC fabricated AA356x coupons were joined to conventional rolled RC5754 material. A set of industry-relevant joint stacks were created. Priority stacks included cast material as the upper layer. More challenging joints were also fabricated with cast material as the lower layer. Automotive industry key performance indicators were used to assess joint integrity. The key results and recommendations were:•HPDC aluminium was revealed to be able to be joined to rolled aluminium according to vehicle manufacturer automotive standards.•Process boundaries were established for satisfactory SPR joints across a range of material thicknesses and stack types.•SPR joint solutions were proven in the most challenging stacks with cast material as a bottom layer.•Greater variability in the joint key performance indicators was observed in stacks where the cast alloy is the top layer.•Microstructural analysis of both AA356x and RC5754 revealed differences in grain structure and hardness and it is proposed that this accounts for the increased variability.•Strength testing of lap shear joints demonstrated the mechanical effectiveness of an SPR joint including cast material. Under normal vehicle operating conditions, the performance of joints including cast material was equivalent to that of rolled material only joints. Following yielding, joints including cast material suffered a more brittle failure mode leading to differences in performance under crash scenarios.

Parts repairing and microstructural refinement of high-pressure die cast aluminum alloys through friction stir processing for bulk production

A key challenge in the production of high-grade automotive aluminum components through the High-Pressure Die Casting (HPDC) process is the imperative to minimize imperfection. In addressing this concern, this study utilizes friction stir processing (FSP), a widely recognized intense plastic deformation technique. FSP is applied to systematically alter the microstructure of HPDC Al-4Mg-2Fe, a prominent alloy extensively used in the die-casting sector. By using the pass strategy to incorporate both one-pass and two-pass approaches, the microstructure is selectively altered to establish a defect-free processed zone. The utilization of FSP demonstrates its efficacy in breaking aluminum dendrites and acicular silicon particles, leading to a uniformly dispersed arrangement of equiaxed silicon particles within the aluminum-based matrix. In addition, FSP eradicates porosity and disintegrates needle-like Fe particles, resulting in a more refined and homogeneously distributed structure. Subsequently, the material's mechanical properties processed by FSP were assessed in the longitudinal direction concerning the processing axis and then compared with those of the original base material.The microstructural refinement and reduction in porosity induced by FSP result in a notable enhancement in hardness, with an increase of 23 % after one pass and 37 % after two passes. The substantial improvement in mechanical properties during the FSP process is predominantly attributed to modifications in the morphology, refinement, and dispersion of intermetallic particles within the matrix. This improvement is further complemented by the ultrafine dispersion of casting defects.This study underscores the efficacy of FSP as a valuable tool for modifying microstructures and improving mechanical properties in HPDC Al-4Mg-2Fe alloys. Such advancements align with the lightweighting objectives pursued by the automotive industry.

Research Progress on Thermal Conductivity of High-Pressure Die-Cast Aluminum Alloys

High-pressure die casting (HPDC) has been extensively used to manufacture aluminum alloy heat dissipation components in the fields of vehicles, electronics, and communication. With the increasing demand for HPDC heat dissipation components, the thermal conductivity of die-cast aluminum alloys is paid more attention. In this paper, a comprehensive review of the research progress on the thermal conductivity of HPDC aluminum alloys is provided. First of all, we introduce the general heat transport mechanism in aluminum alloys, including electrical transport and phonon transport. Secondly, we summarize several common die-cast aluminum alloy systems utilized for heat dissipation components, such as an Al–Si alloy system and silicon-free aluminum alloy systems, along with the corresponding composition optimizations for these alloy systems. Thirdly, the effect of processing parameters, which are significant for the HPDC process, on the thermal conductivity of HPDC aluminum alloys is discussed. Moreover, some heat treatment strategies for enhancing the thermal conductivity of die-cast aluminum alloys are briefly discussed. Apart from experimental findings, a range of theoretical models used to calculate the thermal conductivity of die-cast aluminum alloys are also summarized. This review aims to guide the development of new high-thermal-conductivity die-cast aluminum alloys.

Enhanced toughness and tear resistance of thin-walled High-Pressure Die-Cast aluminum alloys through Friction stir processing

In this study, we investigate the toughness and resistance to tear of thin-wall high-pressure die-cast (HPDC) aluminum alloys in two different orientations following the implementation of friction stir processing (FSP). The FSP technique was applied to two different HPDC Al-Si alloys: the recyclable-grade, high iron, A380 alloy and the premium-quality, low iron, Aural-5 alloy. Our findings reveal significant tear resistance and strength enhancements for both alloys after FSP modification. Specifically, FSPed A380 alloy requires 126% higher energy to tear, and it has 49% higher tear strength than the HPDC counterpart. Similarly, the tear energy and tear strength of the Aural-5 alloy witness enhancements of 69% and 21%, respectively. These findings emphasize the capability of FSP to improve the toughness of HPDC aluminum alloys, creating new possibilities for preventing cracks in a variety of engineering applications.

Ductile fracture prediction of HPDC aluminum alloy based on a shear-modified GTN damage model

In this paper, we investigate how the shear-modified Gurson-Tvergaard-Needleman (GTN) model can be used to reveal the effect of manufacturing-process-induced porosity on the scatter of ductile fracture properties of a high-pressure die-casting aluminum alloy. The GTN model exhibits great advantages in predicting the variation of failure strain/displacement by altering the initial void volume fraction (f0), compared with uncoupled ductile damage models. For a specific metallic material, one unique set of model parameters is usually determined from experiments, which leads to the fact that only a deterministic failure strain/displacement can be obtained under a fixed porosity. To overcome this shortcoming of the shear-modified GTN model, a novel parameter calibration scheme is proposed and validated in the present study. Following the physical background of the GTN model, the twelve material parameters of the shear-modified GTN model have been determined based on a combination of macroscopic mechanical tests covering a wide range of stress states and micromechanics-based unit cell simulations. Different from the existing calibration strategies, the simulation results of unit cells embedded with a spherical void have revealed a mutual dependence between the f0 and critical void volume fraction (fc). By conducting interrupted shear tests, the evolution of secondary nucleated void volume fraction was identified according to the statistical results of the fractured brittle silicon particles. The remaining parameters have been further iteratively determined. In the end, the effectiveness of the proposed parameter determination approach is confirmed based on the accurate prediction of stochastic ductile failure properties (both the global failure displacements and the local failure patterns) in different fracture tests. Given the proposed parameters identification strategy, the GTN material models have been enriched to predict the ductile failure behavior of metallic materials, which possess relatively high porosities and more pronounced scattering in failure properties.

Integrated fatigue life predictions of aluminium castings using simulated local microstructure and defects

In this work, an integrated simulation approach previously developed for static FE analyses is extended to microstructure- and defect-based fatigue life assessments of castings. The approach, the closed chain of simulations for cast components, combines casting process simulation with microstructure modelling and local material characterisation to generate heterogeneous material data for FE analysis and fatigue life assessment. The method is demonstrated on a High-Pressure Die Cast aluminium component. Areas with a high risk of defects are identified based on the simulated solidification conditions, and heterogeneous material data for the fatigue life analysis is generated. Fatigue testing has been performed with different levels of porosities to quantify the effect of defects on the element-specific Wöhler curves. Pore characteristics are assessed using 2D X-ray, fracture surface analysis and Kitagawa diagram. The results highlight the importance of taking the risk of defect formation into consideration when designing industrial aluminium castings subjected to fatigue loads.

Effects of die-casting defects on the blister formation in high-pressure die-casting aluminum structural components

The following work aims to present the casting defects effect in AlSi10MnMg alloy structural components on the blister’s possibility. Structural components must exhibit high mechanical properties, specifically high ductility. That requires the heat treatment process. However, the component’s exposure to high temperatures can cause blistering on the surface, which is unacceptable in the final product.For microstructure studies, the samples were cut from regions close to the gating system (hot areas) and those away from it (cold areas). For comparison, the paper studied castings in the as-cast state and after T7 heat treatment. The results suggest that the blistering process begins at casting defects, which create microstructural discontinuities. If gases are present in a discontinuity, they expand during solution treatment, forming surface blisters. The largest blisters form on cold flakes, mainly in casting areas near the gating system.However, smaller blisters form on porosity - both gas and shrinkage. The last casting defects that act as blistering sites are cold drops, cold shots, and thin oxide films occurring mainly in areas away from the gating system.

The quality improvement of welded joints of die-cast Al alloys using oscillation and current modulation of the electron beam

The issues of the difficult weldability of the high-pressure die-cast aluminum alloys - AlSi10Mg(Fe) were studied within the presented paper. The metallographic, CT, and EDX analyses of castings were performed to identify potential origins of weld joint imperfections and deteriorated weldability. A comparative welding test of welding gravitation die-cast alloys was accomplished to review the influence of the melting process on the weld quality. The casting process was analyzed and several mediums were evaluated as potential sources of material contamination. The selected contaminants were intentionally introduced into the weld joints. The research on welding process improvement and the reduction of the susceptibility to the presence of impurities was accomplished in the next step. The aim of the experiments was the use of dynamic deflection of the electron beam and pulse modulation of its power. The influence of different oscillation frequencies, amplitudes, and patterns was examined. The verified technology was developed, based on the achieved results.

Microstructure-refinement–driven enhanced tensile properties of high-pressure die-cast A380 alloy through friction stir processing

This work employs friction stir processing (FSP), a well-known severe plastic deformation technique, to selectively modify the microstructure of thin-walled, high-pressure die-cast (HPDC) aluminum alloy A380, a major HPDC alloy fabricated in the die casting sector. FSP effectively breaks down Al dendrites and acicular Si particles, creating a homogenized distribution of equiaxed Si particles in the aluminum matrix. After FSP, the refined Si particles (~1.5 μm) are smaller than the eutectic Si particles (3–8 μm) in HPDC condition. In addition, interparticle distance has decreased almost 50% compared to dendritic arm spacing, and FSP has reduced the aspect ratio of Si particles to ~2. Furthermore, FSP eliminates porosity, and breaks down needle-like second-phase Fe-Mn and Cu-rich particles, yielding a refined, homogeneous distribution. The FSP-induced microstructural refinement and porosity reduction improve bulk yield strength and ductility by 23% and 66%. Tensile properties are enhanced beyond those of the die skin of the HPDC plate, and the alloy possesses lower defect density and a highly refined microstructure. This study establishes the viability of FSP as a tool for microstructure modification and mechanical property improvement for HPDC Al alloys for the light-weighting goal of the automotive industries.

Evaluating the Joinability of Thin-Walled High Pressure Die Cast Aluminium for Automotive Structures Using Self-Piercing Rivets

Evaluating the Joinability of Thin-Walled High Pressure Die Cast Aluminium for Automotive Structures Using Self-Piercing Rivets

Subsurface Microstructural Evolution of High-Pressure Diecast A365: From Cast to Cold-Sprayed and Heat-Treated Conditions

The use of cold spray deposition, coupled with diffusion-driven thermal postprocessing, is considered herein as a surface modification process such that near-surface microstructural, micromechanical, and microchemical property improvements can be procured for cost-effective and common aluminum alloy castings. Since the present work was an exploratory investigation into the realm of cold spray induced, high-pressure diecast aluminum subsurface property development and evolution, as well as surface modification, one significant aim was to formalize a set of fundamental observations for continued consideration of such an approach to achieving premium aluminum alloy properties from cost-effective alternatives. Nickel, copper, and titanium cold spray modified near-surface regions of the cost-effective high-pressure diecast A365 system was considered. Near-surface, subsurface, and surface evolution was documented across each of the three pure metal coatings. The analysis was continued across two postprocessing coating-substrate atomic diffusion inspired heat-treated conditions as well. Using energy-dispersive X-ray spectroscopy, field-emission scanning electron microscopy, optical microscopy, and various insights gleaned from an original contextualization of the relevant cold spray literature, noteworthy results were recorded and discussed herein. When copper feedstock was employed alongside thermal postprocessing, diverse surface-based intermetallic compounds formed alongside exotic diffusion zones and severely oxidized regions, thus eliminating thermally activated copper cold-sprayed consolidations from future work too. However, both nickel and titanium cold spray surface modification processing demonstrated potential and promise if correct processing stages were performed directly and chronologically. Consequently, a platform is presented for further research on cold sprayed surface microstructural and property modification of cost-effective alloyed aluminum castings.

Relative Performance of Additively Manufactured and Cast Aluminum Alloys

Laser power bed fusion (LPBF) enables the possibility to improve the performance of critical automotive components by leveraging new design and manufacturing potentials. While the LPBF approach taps into numerous design freedom advantages, the finely focused energy input source, layer-wise thermal cycling, and rapid cooling rates also impact the properties of a given material, thereby affecting performance characteristics of the end-product. The microstructure and mechanical properties of LPBF components must hence be thoroughly compared with the traditional processing technique used for a given application to evaluate its feasibility. In the context of this work, AlSi10Mg processed via LPBF is compared to a high-pressure die-cast aluminum alloy to compare the performance toward technology adoption in manufacturing automotive transmissions. It was found that, with proper process control, LPBF parts can achieve better or comparable density of 99.84–99.95% (cast: 99.15–99.97% cast), similar surface topography, comparable hardness of 54.3–69.3 HRB (cast: 72.8–81.5 HRB), comparable specific wear rates of 3.92*10−4 to 6.04*10−4 mm3N−1m−1 (cast: 2.50*10−4 to 2.55*10−4 mm3N−1m−1), and an overall better corrosion resistance compared to the cast pump housing. The findings show that, with an appropriate selection of process parameters, it is feasible to pursue and possibly enhance the performance of AlSi10Mg for fluid power applications using LPBF.

Improved prediction of low-cycle fatigue life for high-pressure die-cast aluminium alloy AlSi9Cu3 with significant porosity

The fatigue life of a high-pressure die-cast alloy, AlSi9Cu3, with significant porosity is investigated. Standard specimens were cyclically loaded (R = –1) until fatigue rupture occurred. The specimens were μ-CT scanned to obtain a 3D representation of the pores. Models were used to computationally predict the fatigue life using two different methods. First, the fatigue life was predicted using a notch-strain approach combined with a Coffin-Manson durability relationship for homogeneous material. Second, the fatigue life was predicted using an homogenised un-notched model that was combined with an adapted Coffin-Manson relationship which considered a fatigue life reduction due to different pore effects.

Residual stress, microstructure, and mechanical properties analysis of HPDC aluminum engine block with cast-in iron liners

During the manufacturing of cast aluminum (Al) engine blocks with iron (Fe) cylinder liners, the mismatch of thermal expansion/contraction coefficients between the Al cylinder wall and the Fe liners results in the development of high residual strains/stresses. This evolution of residual stress can surpass the strength of the currently used alloys and can lead to the premature failure of the engine block. Thus, improving the mechanical properties of the engine block alloys reduces the number of failures and allows automotive manufacturers to increase the operating pressures and, therefore, efficiency. High-pressure die casting (HPDC) has been shown to provide increased cooling rates in the casting as compared to sand casting, and therefore manufacturers commonly use this method for improving not just the efficiency of the high-volume production, but also mechanical properties of the cast components. Hence, investigating the impacts of the HPDC process on the evolution of residual stress in engine blocks with Fe liners and, consequently, their durability is of great importance. The present study includes a microstructural, mechanical property, and residual strain analysis on an inline-4 HPDC Al engine block with cast-in Fe liners. The results indicate that the yield and tensile strength at the top of the cylinder were ∼15 % and ∼8 % greater than the bottom, respectively. This trend was primarily attributed to the higher cooling rate experienced by the top region. Moreover, the top and bottom of the Fe liner experienced 450 MPa of compressive residual stress in the axial direction, which is counterbalanced by tensile stresses in the Al cylinder bridge (CB), which reaches approximately 70 % of the alloy’s yield strength. The findings of this study provide automotive industries with important insights on the combined impacts of the HPDC process and cast-in Fe liner on the as-manufactured properties of engine blocks and will assist them in developing the next generation of engine blocks.

Characteristics of Al-Si Alloys with High Melting Point Elements for High Pressure Die Casting.

This paper is devoted to the possibility of increasing the mechanical properties (tensile strength, yield strength, elongation and hardness) of high pressure die casting (HPDC) hypoeutectic Al-Si alloys by high melting point elements: chromium, molybdenum, vanadium and tungsten. EN AC-46000 alloy was used as a base alloy. The paper presents the effect of Cr, Mo, V and W on the crystallization process and the microstructure of HPDC aluminum alloy as well as an alloy from the shell mold. Thermal and derivative analysis was used to study the crystallization process. The possibility of increasing the mechanical properties of HPDC hypoeutectic alloy by addition of high-melting point elements has been demonstrated.

Fatigue Design with High Pressure Die Cast Aluminum Including the Effects of Defects, Section Size, Stress Gradient, and Mean Stress

Defects in metallic components can be formed in many manufacturing techniques, including casting, additive manufacturing, and powder metallurgy. These imperfections can significantly affect the mechanical properties, especially fatigue behavior of industrial components. Therefore, it is necessary to evaluate these defects and study their effect on the final mechanical performance of the components. In this study, the effect of defects on fatigue behavior of cast A356-T6 aluminum alloy, as an illustrative material, was investigated. Fatigue tests were conducted under different loading conditions to investigate the effects of defects, specimen size, mean stress and stress gradient. To achieve this goal, fully-reversed uniaxial fatigue tests were conducted on two specimen sizes, as well as tension-tension fatigue tests to study mean stress effect. Rotating bending tests were also performed to study the effect of stress gradient on fatigue performance of materials containing defects. The scatter in fatigue life data was evaluated using statistical analysis. Good correlations of the fatigue life of the specimens under different stress ratios were obtained using a mean stress correction factor. The fatigue life of the specimens under different testing conditions were also estimated using the maximum defect size observed on fracture surfaces.

Characterization and Analysis of Porosities in High Pressure Die Cast Aluminum by Using Metallography, X-Ray Radiography, and Micro-Computed Tomography.

Mechanical performance of cast aluminum alloys is strongly affected by the defects formed during solidification. For example, fractography studies of the fatigue specimens have shown that fatigue failure in aluminum castings containing defects is almost always initiated from defects, among which pores are most detrimental. However, elimination of these pores is neither always economically nor technically possible. This work characterizes defects in high pressure die cast aluminum alloy as an illustrative material, but the methods used can be applicable to other types of castings and defects. The defects were evaluated using metallography as well as micro-computed tomography techniques. The variability of defects between the specimens of two sizes as well as different porosity levels are studied statistically. The distributions of defects based on location within the specimens are also analyzed. Moreover, the maximum defect size within the specimens are estimated using extreme value statistics, which can be used as an input to fatigue life prediction models. Extreme value statistics is applied on both 2D and 3D defect data. The accuracy of each approach is verified by comparing the estimated maximum defect size within the specimens with the maximum observed defects on fracture surfaces of fatigue specimens.

Creep behavior of high-pressure die-cast AlSi10MnMg aluminum alloy

High-pressure die-cast (HPDC) AlSi10MnMg (AA365) has been widely used in the manufacturing of automotive components because it has excellent castability, is lightweight, and possesses good mechanical strength. In particular, this alloy must be capable of withstanding long-term exposure to high temperatures in order for these automobile parts to be useable. To investigate the viscoelastic behavior of HPDC AA365 with the aim of improving the long-term structural performance at high temperatures, we performed a creep test in the temperature range of 373–573 K with a constant applied stress of 64–217 MPa. A micro-hardness test of the HPDC AA365 alloy, performed after the creep test, yielded hardness values of 64.0 HV and 49.9 HV for the gauge and grip sections, respectively. The observed grain-size differences between the sections may have led to this difference in micro-hardness. Moreover, both values of micro-hardness were relatively low compared with the value of 93.5 HV for HPDC AA365 before the creep test. This was because of recovery and recrystallization. The creep tests also showed that the minimum creep rate increased with increasing applied stress for each temperature, causing a decrease in the time to failure. Based on the true stress exponent (n) on a scale of 1 to 90, various creep mechanisms for HPDC AA365 were revealed, including the Harper-Dorn, dislocation, and power-law breakdown mechanisms. The specific creep mechanism depended on temperature and applied stress. Furthermore, owing to the presence of the threshold stress, the apparent creep activation energy (259.08 kJ/mol) was substantially higher than that of aluminum (Al) self-diffusion (Qd = 143 kJ/mol). The existence of the threshold stress can also be demonstrated by a high n value that does not correspond to the n of pure Al under certain conditions. Failure in these alloys can be caused by void coalescence, cracked-brittle Si particles, and intermetallic phases that served to initiate and propagate the crack. Our results demonstrated that the fracture mechanism changed from transgranular to intergranular fracture in response to the applied stress and temperature. Our findings can improve the applications of high-pressure die-cast aluminum alloys.