Development of a high strength Al-Mg2Si-Mg-Zn based alloy for high pressure die casting

A high strength Al-Mg2Si-Mg-Zn based alloy has been developed for the application in high pressure die casting to provide improved mechanical properties. The effect of various alloying elements on the microstructure and mechanical properties including yield strength, ultimate tensile strength and elongation of the alloy was investigated under the as-cast and heat-treated conditions. The typical composition of the high strength alloy has been optimised to be Al-8.0wt%Mg2Si-6.0wt%Mg-3.5wt%Zn-0.6wt%Mn (Al-11.0wt%Mg-2.9wt%Si-3.5wt%Zn-0.6wt%Mn) with unavoidable trace impurities. The mechanical properties of the alloy were enhanced by a quick solution treatment followed by ageing treatment. The improved tensile properties were at a level of yield strength over 300MPa, the ultimate tensile strength over 420MPa and the elongation over 3% assessed using international standard tensile samples made by high pressure die casting. The microstructure of the die-cast alloy consisted of the primary α-Al phase, Al-Mg2Si eutectics, AlMgZn intermetallics and α-AlFeMnSi intermetallics under the as-cast condition. The AlMgZn intermetallic compound was dissolved into the Al-matrix during solution treatment and subsequently precipitated during ageing treatment for providing the effective improvement of the mechanical properties.The financial support is gratefully acknowledged for the Engineering and Physical Sciences Research Council (EPSRC) (Project number: EP/I038616/1), Technology Strategy Board (TSB) (Project number: 101172) and Jaguar Land Rover (JLR), United Kingdom

Effect of nickel on the microstructure and mechanical property of die-cast Al–Mg–Si–Mn alloy

The effect of nickel on the microstructure and mechanical properties of a die-cast Al–Mg–Si–Mn alloy has been investigated. The results show that the presence of Ni in the alloy promotes the formation of Ni-rich intermetallics. These occur consistently during solidification in the die-cast Al–Mg–Si–Mn alloy across different levels of Ni content. The Ni-rich intermetallics exhibit dendritic morphology during the primary solidification and lamellar morphology during the eutectic solidification stage. Ni was found to be always associated with iron forming AlFeMnSiNi intermetallics, and no Al3Ni intermetallic was observed when Ni concentrations were up to 2.06 wt% in the alloy. Although with different morphologies, the Ni-rich intermetallics were identified as the same AlFeMnSiNi phase bearing a typical composition of Al[100–140](Fe,Mn)[2–7]SiNi[4–9]. With increasing Ni content, the spacing of the α-Al–Mg2Si eutectic phase was enlarged in the Al–Mg–Si–Mn alloy. The addition of Ni to the alloy resulted in a slight increase in the yield strength, but a significant decrease in the elongation. The ultimate tensile strength (UTS) increased slightly from 300 to 320 MPa when a small amount (e.g. 0.16 wt%) of Ni was added to the alloy, but further increase of the Ni content resulted in a decrease of the UTS.The Engineering and Physical Sciences Research Council (EPSRC), Technology Strategy Board (TSB) and Jaguar Land Rover (JLR) in the United Kingdom

Grain boundary precipitation induced by grain crystallographic misorientations in an extruded Al-Mg-Si-Cu alloy

The grain boundary precipitation induced by grain crystallographic misorientations in an extruded Al-Mg-Si-Cu alloy was investigated by electron back-scattering patterns and high resolution transmission electron microscopy. The results showed that compared with the recrystallization cube {1 0 0}〈0 0 1〉 texture, the deformation brass {1 1 0}〈1 1 2〉 texture prevailed in the microstructure. The brass texture mainly contributed for the formation of low angle grain boundaries, where the pre-β″/β′ phases were formed during precipitation. The recrystallization cube texture predominately induced the formation of high angle grain boundaries, where the Q′/Q phases related to the corrosion were precipitated. And, high and low grain boundary was 23.5% and 76.5% proportion in the microstructure, respectively. Finally, it was believed that in order to improve the resistance to intergranular corrosion of alloy, the recrystallization cube {1 0 0}〈0 0 1〉 texture should be inhibited as far as possible.Hunan Provincial Innovation Foundation for Postgraduate (CX2010B044), P.R. China

Insight into the partial solutionisation of a high pressure die-cast Al-Mg-Zn-Si alloy for mechanical property enhancement

Engineering and Physical Sciences Research Council, United Kingdom; National Natural Science Foundation of China; Natural Science Basic Research Plan in Shaanxi Province of Chin

Repeatability of tensile properties in high pressure die-castings of an Al-Mg-Si-Mn alloy

© 2015 The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht High pressure die-castings of an Al-Mg-Si-Mn alloy have been assessed in terms of the repeatability of the mechanical properties including yield strength, ultimate tensile strength and elongation by the normal standard deviations method and by the Weibull statistical model with three parameters. It was found that the round samples had the maximum Weibull modulus, indicating the best repeatability. The machined samples exhibited the second best of Weibull modulus. Among the square samples, the 2 mm and 5 mm thick samples had the lowest and the highest Weibull modulus respectively, indicating that the repeatability for the castings was influenced by the wall thickness. The microstructural uniformity and porosity levels are critical factors in determining the repeatability of the high pressure die-castings. A less segregation in the microstructure could uniform the stress distribution in the die-castings and a less porosity in the casting could reduce the sources for brittle fracture. These improved the repeatability in casting production.The authors acknowledge the Engineering and Physical Sciences Research Council (EPSRC), Technology Strategy Board (TSB) and Jaguar Land Rover (JLR) in United Kingdom for financial support

In-situ Mo nanoparticles strengthened CoCrNi medium entropy alloy

In present work, the CoCrNi/Mo mixed powder was designed and fabricated by a novel coating method followed by the calcination and reduction processes. The results indicated that in-situ Mo particles distributed homogeneous among the CoCrNi gas atomized powder and no other drawbacks generated such as contamination and oxidation, the reduced Mo particles were nanoscale, and maximum size did not exceed 600 nm. The SPSed CoCrNi/Mo composite with significant amount of in-situ μ phases showed improved mechanical properties: the yield strength and hardness from 352 MPa to 159 HV to 815 MPa and 375 HV, compared with the pure CoCrNi MEA (medium entropy alloy). The improved properties are mainly attributed to synergistic effects of various strengthening mechanisms, including solid solution strengthening, load transfer effect, Orowan strengthening, grain refinement, especially thermal mismatch mechanism. In addition, this could give insights on the applications of other MEA or HEA-based composites fabricated by coating method.National Natural Science Foundation of Chin

An Overview on the Process Development and the Formation of Non-Dendritic Microstructure in Semi-Solid Processing of Metallic Materials

Semi-solid metal (SSM) processing has been an attractive method for manufacturing near-net-shape components with high integrity due to its distinct advantages over conventional forming technologies. SSM processing employs a mixture of solid phase and liquid metal slurries and/or non-dendritic feedstocks as starting materials for shaping. Since the original development from 1970s, a number of SSM processes have been developed for shaping components using the unique rheological and/or thixotropic properties of metal alloys in the semi-solid state, in which the globular solid particles of primary phase are dispersed into a liquid matrix. In this paper, the progress of the development of shaping technologies and the formation of non-dendritic microstructure in association with the scientific understanding of microstructural evolution of non-dendritic phase are reviewed, in which the emphasis includes the new development in rheomoulding, rheo-mixing, rheo/thixo-extrusion and semi-solid twin roll casting, on the top of traditional rheocasting, thixoforming and thixomoulding. The advanced microstructural control technologies and processing methods for different alloys are also compared. The mechanisms to form non-dendritic microstructures are summarised from the traditional understanding of mechanical shear/bending and dendrite multiplication to the spheroidal growth of primary phase under intensively forced convection. In particular, the formation of spheroidal multiple phases in eutectic alloys is summarised and discussed. The concluding remarks focus on the current challenges and developing trends of semi-solid processing

A casting magnesium alloy for providing improved thermal conductivity

PatentThe invention relates to a casting magnesium alloy, in particular the alloy that can provide significantly improved thermal conductivity in comparison the commonly used AZ91D magnesium alloys. The typical thermal conductivity is at a level of 110 W/m.K, which is close to the thermal conductivity of the commonly used A380 aluminium alloy

A casting alloy

A casting Al-Si based alloy providing improved mechanical properties at elevated temperatures while maintaining acceptable mechanical properties at ambient temperature, consists of the following elements (in weight percent): Silicon from 7 to 10, Copper from 2 to 4.5 where Si=6+Cu, Magnesium from 0.1 to 0.7 where 2.5≤(Cu+Mg)≤4.5, Ti from 0.1 to 0.3, Zr from 0.15 to 0.8, Mn from 0.05 to 0.2, Sr from 0.01 to 0.02, Ni less than 0.02, Cr less than 0.01, Fe less than 0.15, and the remainder is aluminium and inevitable impurities

Ultrastrong and ductile synergy of additively manufactured H13 steel by tuning cellular structure and nano-carbides through tempering treatment

Microstructural evolution and mechanical properties of H13 steel fabricated by selective laser melting (SLM) with subsequent tempering treatment were systematically examined. It was found that the microstructure of the as-SLMed H13 samples consisted of cellular structures, lath martensite and high-volume fraction of retained austenite. After tempering at 600 °C for 1 h, the nanoscale Cr23C6 particles were detected at the boundaries of the partially dissolved cellular structures. The fine grains, the retained cellular structures, and the formation of Cr23C6 carbides significantly improved the mechanical properties of the H13 steel. A superior mechanical properties, including the yield strength (YS) of 1647 ± 29 MPa, ultimate tensile strength (UTS) of 2013 ± 35 MPa and elongation (El) of 4.1 ± 0.3% have been achieved in the SLMed H13 steel after tempering at 600 °C for 1 h. With the increase of tempering temperature to 700 °C, the cellular structures were completely dissolved and the high number density of coarse Cr23C6 carbides were formed, which led to the decrease of UTS at 1083 ± 21 MPa, while the elongation was significantly improved to 12.3 ± 1.2% due to the recovery of dislocation density and the decomposition of martensite in the H13 steel