Cast Al Si Research Articles

Coupling CALPHAD Method and Entropy-Driven Design for the Development of an Advanced Lightweight High-Temperature Al-Ti-Ta Alloy

In this study, a new lightweight Al-Ti-Ta alloy was developed through a synergistic approach, combining CALPHAD methodology and entropy-driven design. Following compositional optimization, the Al87.5Ti6.25Ta6.25 (at.%) alloy was fabricated and isothermally heat-treated at 475 °C for 24 h to attain equilibrium. X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) analyses revealed a dual-phase microstructure comprising a 50 vol.% FCC matrix enriched in Al and 50 vol.% Al3(Ti,Ta)-type intermetallic phase (IP). Notably, the FCC phase exhibited a high-melting transition temperature of 660 °C, surpassing conventional Al-Si cast alloys. Phase-specific nanomechanical properties were evaluated using Nanoindentation. Microindentation tests demonstrated exceptional microhardness of approximately 3300 MPa. These results indicate the alloy’s superior hardness compared to conventional alloys such as Al-Si (A390), 7075 Al alloy, and CP-Ti, even exceeding Ti-64 alloy at a 15% lower density. The alloy’s stability under prolonged heat treatment at 475 °C, reflected by stable phases, microstructure, and mechanical properties, highlights its enhanced thermal stability, which can be attributed to entropy-driven phase stabilization. This study underscores the effectiveness of integrating entropy-driven design strategy with CALPHAD predictions for the accelerated development of advanced Al-based alloys.

Highlights on the Role of Fe, Sr, and Solidification Time on Porosity Formation in Al–Si Cast Alloys

Highlights on the Role of Fe, Sr, and Solidification Time on Porosity Formation in Al–Si Cast Alloys

Effects of Zr and Sr on microstructure and mechanical properties of cast Al–Si–Cu–Ni–Mg alloy

Effects of Zr and Sr on microstructure and mechanical properties of cast Al–Si–Cu–Ni–Mg alloy

Effect of loading conditions on short fatigue crack propagation behaviours in cast Al[sbnd]Si alloys

The effect of loading conditions on short crack propagation behaviours in cast AlSi alloys was investigated by a combination of photo-microscopy monitoring and post mortem analysis. The findings suggest that the path of short cracks is minimally influenced by loading conditions, whereas loading conditions significantly affect the fatigue crack growth rate (FCGR) and its statistical characteristics. Crack closure effect is observed under zero and negative stress ratio conditions. Roughness-induced crack closure occurs due to the coarse grain microstructure of cast AlSi alloys and the Stage-I mode growth of cracks within grains in the microstructural short crack regime. The high level of plasticity around the crack tip under negative stress ratio conditions has a significant impact on FCGR, resulting in a negative crack opening stress. When the stress ratio exceeds approximately 0.3, short cracks exhibit no crack closure. The load-level effect is observed only at high load conditions with negative stress ratios. Finally, a probabilistic short crack growth model was established using a Bayesian linear regression model to analyse the effect of stress ratio on the uncertainty of FCGR. After considering the crack closure effect, the difference in distributions of FCGR model parameters decreases significantly among different stress ratio conditions.

Plasma Electrolytic Oxidation (PEO) as a Promising Technology for the Development of High-Performance Coatings on Cast Al-Si Alloys: A Review

Cast Al-Si alloys, recognized for their excellent mechanical properties, constitute one of the most widely employed non-ferrous substrates in several sectors, and are particularly relevant in the transport industry. Nevertheless, these alloys also display inherent limitations that significantly restrict their use in several applications. Among these limitations, their low hardness, low wear resistance, or limited anti-corrosion properties, which are often not enough when the component is subjected to more severe environments, are particularly relevant. In this context, surface modification and the development of coatings are essential for the application of cast Al-Si alloys. This review focuses on the development of coatings to overcome the complexities associated with improving the performance of cast Al-Si alloys. Against this background, plasma electrolytic oxidation (PEO), an advanced electrochemical treatment that has revolutionized the surface modification of several metallic alloys in recent years, emerges as a promising approach. Despite the growing recognition of PEO technology, the achievement of high-performance coatings on cast Al-Si is still a challenge nowadays, for which reason this review aims to provide an overview of the PEO treatment applied to these alloys. In particular, the impact of the electrolyte chemical composition on the properties of the coatings obtained on different alloys exposed to harsh environments has been analyzed and discussed. By addressing the existing gaps and challenges, this paper contributes to a better understanding of the intricacies associated with the development of robust PEO coatings on cast Al-Si alloys.

Multipass friction stir welding of dissimilar Al–Si and Al–Mg cast aluminum alloys

In this study, dissimilar cast Al–Si and Al–Mg alloys were joined together using friction stir welding (FSW) technique, employing different levels of heat input and various numbers of FSW passes. For this purpose, two sets of welds were prepared with either low or high heat inputs. Each sets consisted of three welds with one, two, or three FSW passes. The microstructure of the welds was examined using optical and scanning electron microscopes on the weld cross section. The phases in the stirred zone (SZ) were identified using x-ray diffraction method. Hardness profiles and tensile properties were examined to understand joint efficiency. Based on the microstructural analysis results, three distinct regions were identified in the SZ of all welds, including the deformed Al–Mg base metal (region 1), the deformed Al–Si base metal (region 2), and the region with interdiffusion of the two base metals (region 3). Increasing the number of FSW passes increases the fraction of region 3 in the SZ, indicating enhanced stirring and interdiffusion of the two base metals. Following these microstructural changes in the SZ, the welds exhibited a significant improvement in strength and ductility with an increasing number of FSW passes and heat input. The weld with three FSW passes and higher heat input demonstrated the highest strength and ductility, reaching the strength of 187 MPa and ductility of 8.3 % which corresponded to 92 % of the strength and 106 % of the ductility of the Al–Si (the weaker) base metal, respectively. It was concluded that an increase in the number of FSW passes, altered the bonding mechanism from predominantly mechanical interlocking in single-pass welds to robust metallurgical bonding in three-passes welds.

Microstructure evolution and mechanical properties of Al-12Si-xCu-yNi-1Mg alloy with different Ni/Cu ratios

High-temperature properties are the key factor affecting the industrial application of cast Al-Si alloy. In this paper, four kinds of Al-12Si-xCu-yNi-1Mg (y = 7.5-x, x:4.84, 5.17, 5.55, 6.00.) alloys were prepared by changing the Ni/Cu ratio and regulating the type and proportion of the heat-resistant phase, and then systematically analyzed the changing of microstructure and mechanical properties and clarified the heat resistance mechanism of the alloy. The experimental results show that with the increase of the Ni/Cu ratio, the eutectic Si phase of the as-cast alloys was refined, the blocky Al2Cu phase and the strip Al7Cu4Ni phase disappeared, and the reticular Al3CuNi heat-resistant phase increased, and the size of Al3CuNi phase decreases first and then increases. After T6 heat treatment, the eutectic silicon spheroidized, and the nickel-rich phase did not change significantly. As the Ni/Cu ratio increases, the tensile strength of the alloy at room temperature increases first and then decreases, and its tensile strength at high temperature increases continuously. When the Ni/Cu ratio is 0.45, and the maximum value of tensile strength at room temperature is 355 MPa. When the Ni/Cu ratio is 0.55, the content of the Al3CuNi phase with high thermal stability is most, and the Al2Cu phase with poor stability is less, so the high-temperature tensile strength is the highest, and the value of tensile strength at 275 °C, 325 °C and 375 °C is 192 MPa, 172 MPa, and 89 MPa, respectively.

Parametric study and optimization of cast Al-Si alloy heat exchanger using Taguchi method

A 3-D numerical model of staggered pin fin array in cast Al-Si alloy heat ex-changer was established. For further structural optimization, seven geometric parameters were studied by Taguchi method, including diameter, width, transverse spacing, longitudinal spacing, offset distance, slit length, and row number. The 32 cases with different geometric parameters were simulated numerically. The heat transfer characteristics, flow resistance characteristics, and overall performance were fully discussed. The diameter and transverse spacing have important influence on heat transfer characteristics, and the structural parameters that affect the resistance characteristics are diameter, longitudinal spacing and slit length. Then analysis of variance shows that diameter and transverse spacing have greater effects on the overall performance than other five parameters. At last, the optimized structure of staggered pin fin array was obtained, and j/f1/3 increased by 1% to 3% for volume flow rate in the range from 0.03 to 0.11 m3/s.

Influence of Modifying Elements on the Structure and Mechanical Properties of Casting Al–Si Alloys

Influence of Modifying Elements on the Structure and Mechanical Properties of Casting Al–Si Alloys

Annealing behavior of AlSi10Mg alloy fabricated by laser powder bed fusion

The AlSi10Mg alloy fabricated by laser powder bed fusion was subjected to isochronal annealing for 2h at temperatures in the range of 100–520 °C. Recovery and grain growth of the annealed samples were investigated by combining EBSD and in situ TEM techniques. A bimodal grain size distribution with grain sizes of 0.9 μm and 2.3 μm was developed in the initial sample, where large grains were found in the interiors of melt pools and most of small grains were distributed along melt pool boundaries. In-situ TEM investigations revealed that nucleation that occurs at the melt pool boundaries is as a consequence of migration of high angle boundaries during annealing. A slight increase in grain sizes was discovered during high-temperature heat treatment, indicating the remarkable thermal stability of the alloy compared to conventional cast Al-Si alloys. This is explained by the fact that the stable eutectic Si structure, which was originally formed during rapid solidification, can effectively retard grain boundary migration during recrystallization.

Effect of rare earth Ce on the microstructure and mechanical properties of cast Al–7Si alloys

Casting experiments were carried out on Al–7Si using different additions of rare earth Ce at a reaction temperature of 1200 K. Based on the ternary phase diagram of Al–Si–Ce, the effects of rare earth Ce on the α-Al grain refinement, the mechanism of the eutectic Si phase modification, as well as on the mechanical properties and fracture morphology of the alloy were investigated. The results show that the addition of rare earth Ce generates a Ce-containing phase inside the alloy, which becomes a heterogeneous core of eutectic Si and changes the nucleation conditions of eutectic Si. The mechanical properties of the alloy were optimal when the Ce addition was 0.2 wt.%, and the defect porosity and average pore area were minimized. Ce-containing phases were found at fracture cracks, and these Ce-containing phases were deviated and aggregated at grain boundaries, which induced defects to be generated, and microcracks were easily produced during plastic deformation, which ultimately led to the fracture of the alloy. According to the growth kinetic relationship, due to the difference of different atomic radii, the inter-atomic forces lead to different nucleation densities of grains. With the generation of Ce-containing phases at the interfaces, the eutectic Si changes its growth direction and grows towards a 70° angle to the original direction with a tighter atomic ordering sequence of the stacking, and more twinned Si is generated and gradually stacked up at the interfaces, which directly alters the morphology of the eutectic Si.

The Fatal Defects in Cast Al-Si Alloys Due to Sn Addition.

Cast defects are common in cast alloys and they are difficult to eliminate without deformation. They strongly degrade the mechanical properties of cast alloys. The addition of some elements can affect the number of cast defects. In this work, the deleterious effect of Sn addition on the mechanical properties of Al-Si alloys has been investigated via 3D-computed tomography, SEM and TEM. Amorphous Sn oxides were found near the alumina film or formed enclosures with alumina film. The melt containing high Sn content was trapped by enclosures, causing more shrinkage pores during solidification. Cracks likely initiated and expanded along these pores and brittle amorphous Sn oxides, deteriorating the mechanical properties. This work suggests not adding Sn to various Al alloys when used in a cast state.

3D Investigation of Damage During Strain‐Controlled Thermomechanical Fatigue of Cast Al–Si Alloys

The strain‐controlled thermomechanical fatigue behavior is investigated for three cast near‐eutectic Al–Si alloys with different Ni, Cu, and Mg contents. Synchrotron tomography and neutron diffraction experiments are used to correlate 3D microstructural features with damage initiation and evolution. The results show that the alloy with lower Cu, Ni, and Mg concentrations has up to 45% higher thermomechanical fatigue resistance for cooling/heating rates of 5 and 15 K s−1. In addition, this alloy also exhibits damage formation at later stages during thermomechanical fatigue and slower damage accumulation compared to other alloys. This difference in behavior is a consequence of its higher ductility, which is a result of the lower volume fraction and global interconnectivity of the 3D hybrid networks formed by Si and intermetallics and the absence of large primary Si clusters which act as preferred crack initiation sites during the early stages of thermomechanical fatigue.

Microstructural effects on short fatigue crack propagation in cast Al-Si alloys

The role of microstructure on the short fatigue crack behaviour of cast Al-Si alloy under high cycle loading conditions is investigated by tracking the progress of cracks through fine, medium and coarse microstructured samples. Generally, in the early stage of crack growth, short cracks mainly grow transgranularly, with cracks growth close to low index crystallographic planes (mainly {100}) in some grains and frequently inhibited at grain boundaries. In the late stage, the crack growth mode gradually shifts from crystallographic stage-I to non-crystallographic stage-II. The short cracks grow faster and fluctuate significantly according to local microstructure. Our results show that finer microstructures offer greater crack nucleation and propagation resistance.

Fretting fatigue behavior and damage mechanism of cast Al-Si-Cu-T6 alloy under two surface roughness conditions

This paper experimentally evaluates the fretting fatigue properties of cast Al-Si-Cu-T6 alloys against nodular cast irons with two surface roughnesses. A softening phenomenon contrary to the cyclic response behavior of plain cyclic loading is pointed out and discovered to be affected by persistent damage and cumulative plastic deformation. Two considerably different roughness conditions produce two entirely distinct damage mechanisms, and a schematic diagram is drawn to illustrate the discrepancy. The initiation and propagation of cracks are not only affected by fretting wear damage but also significantly depend on the microstructure, especially the α-Fe and (β + ω) phases play key roles. The realization of this research comprehensively reveals the fretting damage mechanism of Al-Si cast alloys under two characteristic contact surface states, which serves the fretting failure analysis of aluminum castings in the automotive industry.

Investigation of Phase Transformation and Mechanical Properties of A356 Alloy with Cu and Zr Addition during Heat Treatment

Cast A356(Al-Si-Mg) alloys are widely used in automotive and general applications because of their mechanical properties and castability. Al-Si-Mg-(Cu) alloys typically lose their strength above 170 o C due to coarsening of precipitates, which limits their application to components. To maintain their strength at elevated temperature, Al-Si-Mg-(Cu) alloys are modified by adding transitional metals. Several studies have been carried out to evaluate the effect of Zr addition on the high temperature mechanical properties of cast Al-Si alloys because Zr can form thermally stable phases such as Al3Zr. Despite the relative studies on the influence of Cu and Zr on the mechanical properties of cast Al-Si-Mg-(Cu) alloys, investigations of the effect of Zr on the phase transformations and the mechanical properties during heat treatment remains limited. In this study, the effects of added Cu and Zr on the phase transformations and the mechanical performance during heat treatment of A356 cast alloy were investigated. Needle-like and block-like (Al,Si)3(Ti,Zr) dispersoids formed as some Si and Ti replaced Al and Zr in Al3Zr crystal structures were generally observed. Furthermore, with increasing solution treatment time, the size of Zr dispersoids was reduced, and smaller Zr particles were precipitated at the same time, which caused a decrease in the area fraction of the Zr dispersoids. In addition, the metastable L12 structures of Zr dispersoids in Al-Si-Mg-Cu-Zr alloys were transformed into stable D023 during solution heat treatment as the Cu addition accelerated the transformation. Tensile and low-cycle fatigue (LCF) tests were performed to reveal the effects of (Al,Si)3(Ti,Zr) dispersoids on mechanical properties. As a result, elongation at elevated temperature was highly increased, while maintaining strength, according to the increase in solution heat treatment time, which improved low-cycle fatigue properties.

The effect of thermal exposure on the microstructure and mechanical properties of cast Al-Si alloy for the cylinder head

Cast Al-Si alloy is widely used in cylinder head structures and long-term service in 200–250 °C elevated temperature environments, which is easy to cause the deterioration of alloy properties. In this study, the thermal stability of the alloy during thermal exposure at 200 °C and 250 °C is investigated through the microstructure characterization and the mechanical properties test. The results show that the thermal exposure leads to the damage evolution of the precipitates in the microstructure. With the coarsening of the precipitates, the dislocation changes from cutting precipitates to bypassing precipitates, resulting in a weakening of the precipitation strengthening effect. The T6 alloy is in the insufficient peak aging state, and the alloy first reaches the peak aging state and then enters the over aging stage during the thermal exposure. Overall, with the increase in thermal exposure time and temperature, the Al matrix hardness, ultimate tensile strength (UTS), and yield strength (YS) decrease gradually and finally tend to be stable. As the thermal exposure progresses, the alloy fracture characteristic transitions from brittle fracture to ductile fracture, and the elongation of the alloy increases. In addition, the coarsening process of the thermal exposure alloy is described based on the Lifshitz-Slyozov-Wagner (LSW) theory, and the modified coarsening kinetic model can be divided into the rapid roughening stage and the stable roughening stage. Further, the damage parameter is defined as the relative change of precipitation strengthening to describe the deterioration degree of the mechanical properties for thermal exposure alloy.

Microstructure and Mechanical Properties of Cast Al-Si-Cu-Mg-Ni-Cr Alloys: Effects of Time and Temperature on Two-Stage Solution Treatment and Ageing

Ameliorating the high-temperature performance of cast Al-Si alloys used as engine components is essential. The effects of different T6 heat-treatment processes on the microstructure and mechanical properties of cast Al-Si-Cu-Mg-Ni-Cr alloys were investigated in the present study. The results demonstrate that, under the optimal solution treatment conditions of 500 °C for 2 h and 540 °C for 4 h, the T-Al9FeNi phase was present in the alloy, and the roundness of primary Si and the aspect ratio of eutectic Si in the alloy reached valley values of 1.46 and 2.56, respectively. With increasing ageing time at 180 °C, the tensile strength significantly improved, while the microhardness first increased and then decreased. When the ageing time was 4 h, microhardness reached a peak value of 155.82 HV. The fracture characteristics changed from quasi-cleavage to the coexistence of quasi-cleavage and dimples. After heat treatment, the high-temperature tensile properties of the alloy improved, which is a significant advantage compared to the as-cast alloy. The stable Al3Ni and Al9FeNi phases inhibited the cracking of the alloy at 350 °C.

Influence of Plasma Electrolytic Oxidation of Cast Al-Si Alloys on Their Phase Composition and Abrasive Wear Resistance

The microhardness and abrasive wear resistance of cast Al-Si alloys after plasma-electrolytic oxidation (PEO) in a weakly alkaline basic electrolyte (3 g/L KOH + 2 g/L Na2SiO3), as well as with the addition of H2O2, were determined. X-ray analysis showed that the PEO layer comprises two oxide phases, namely α-Al2O3 and γ-Al2O3, as well as sillimanite -Al2O3 · SiO2 and a small percentage of mullite -3 Al2O3 · 2SiO2. Silicon is present in the structure of the oxide layer, and its percentage is greater than that of the alloys in their initial state. It has been shown that the characteristics of PEO layers on AK9 and AK12 silumins synthesized in an electrolyte of basic composition increase (microhardness up to 900–1000 HV and abrasive wear resistance by 14–57 times). The formation of PEO layers in the base electrolyte with the addition of 3 g/L of hydrogen peroxide intensifies the synthesis process and promotes the formation of high-temperature oxide phases (in particular, corundum). The abrasive wear resistance of both silumins with PEO layers synthesized in such an electrolyte increases by 30–70%.

Effect of thermal degradation on mechanical properties of cast Al-Si alloys for cylinder heads

The effect of thermal degradation on mechanical properties of cast Al-Si alloys for cylinder heads is investigated. Thermal degradation has a significant deteriorating effect on the tensile strength caused by the coarsening and coalescence of the θ phase (Al2Cu) due to precipitation reaction. The dominant factor for degradation at 250 ℃ is exposure temperature, while exposure time has a greater effect at 200 ℃. Thermal degradation increases the long crack growth rate significantly due to the increase in plasticity scale ahead of the crack tip. The effective stress intensity factor range (ΔKeff) is modified for thermally exposed alloys by adding the plasticity zone size to the crack length and considering the reduction in crack resistance from the precipitates.