Conventional Cast Alloy Research Articles

Investigation of wear behaviour of thixoformed and conventional gravity cast AlSi8Cu3Fe alloys

Purpose – In the present work, thixoformed AlSi8Cu3Fe alloy was investigated for its tribological properties. The tribological analysis reveals good sliding wear behaviour for thixoformed alloy due to thixotropic microstructural character. The results are compared with sliding wear behaviour of conventional gravity cast alloy. This paper aims to discuss these subjects. Design/methodology/approach – In this study, thixoforming and gravity casting methods are used to produce materials. The ball-on-disc CSM tribometer was used to carry out the tribological tests that were performed under dry sliding conditions, under two different loads of 1N and 5N. Wear tests were performed first on the conventional gravity cast samples and then on the thixoformed counterparts in exactly the same fashion to facilitate a comparison. The microstructural characterizations are performed in optical microscopy, scanning electron microscopy and energy dispersive X-ray spectrometry. Findings – Thixoformed samples have better wear resistance than conventional gravity cast samples. The wear performance improves in thixoformed AlSi8Cu3Fe alloy thanks to changing the microstructure. The superiority of the former is attributed to its structural features. Originality/value – In this study, the thixoforming of AlSi8Cu3Fe alloy can provide important wear performance in comparison with conventional casting of AlSi8Cu3Fe alloy. This alloy is known to be used widely in automotive industry. Therefore, the alloy is highly exposed to wear and it is thought that thixoforming method can increase the wear resistant.

Microstructure and Mechanical Properties of Rapidly Solidified Al-Fe-X Alloys

Rapidly solidified aluminium alloys have many interesting properties such as higher thermal stability and strength, when compared with conventional cast alloys. Due to these properties, RS alloys seem to be prospective for using in automotive or aircraft industry. Aim of this work was to compare the differences in microstructure of alloys containing Fe, Ni and Cr which were prepared by different solidification rate. Alloys were prepared by melt spinning, melting with follow-up quenching into the water and by conventional casting with pouring into brass mould. Microstructure of prepared alloys was investigated by scanning electron microscope; phase composition was determined by x-ray diffraction. In this experiment, microhardness was measured in the initial state of all types of alloys; rapidly solidified alloys were also annealed to determine thermal stability by microhardness measurement. Results indicate that higher solidification rate refines the microstructure which is composed of supersaturated solid solution of alloying elements in aluminium and stable and meta-stable intermetallic phases. Hardness of the alloys increases and microstructure refines with solidification rate.

Inconel 939 processed by selective laser melting: Effect of microstructure and temperature on the mechanical properties under static and cyclic loading

Nickel-based superalloys, such as Inconel 939, are a long-established construction material for high-temperature applications and profound knowledge of the mechanical properties for this alloy produced by conventional techniques exists. However, many applications demand for highly complex geometries, e.g. in order to optimize the cooling capability of thermally loaded parts. Thus, additive manufacturing (AM) techniques have recently attracted substantial interest as they provide for an increased freedom of design. However, the microstructural features after AM processing are different from those after conventional processing. Thus, further research is vital for understanding the microstructure-processing relationship and its impact on the resulting mechanical properties. The aim of the present study was to investigate Inconel 939 processed by selective laser melting (SLM) and to reveal the differences to the conventional cast alloy. Thorough examinations were conducted using electron backscatter diffraction, transmission electron microscopy, optical microscopy and mechanical testing.It is demonstrated that the microstructure of the SLM-material is highly influenced by the heat flux during layer-wise manufacturing and consequently anisotropic microstructural features prevail. An epitaxial grain growth accounts for strong bonding between the single layers resulting in good mechanical properties already in the as-built condition. A heat treatment following SLM leads to microstructural features different to those obtained after the same heat treatment of the cast alloy. Still, the mechanical performance of the latter is met underlining the potential of this technique for producing complex parts for high temperature applications.

Fine-Grained Bulk NiTi Shape Memory Alloy Fabricated by Rapid Solidification Process and Its Mechanical Properties and Damping Performance

A near-equiatomic NiTi shape memory alloy was fabricated by rapid solidification process through vacuum arc melting followed by vacuum suction casting in water-cooled thick copper mold. The rapidly solidified (or suction cast) NiTi alloy shows much finer grains and homogenous microstructure, in particular a uniform distribution of various fine precipitates, compared to the conventional cast one. The resultant alloy also exhibits the homogenous Ni distribution in the matrix of the alloy, allowing the martensitic transformation to take place throughout the NiTi alloy matrix simultaneously and resulting in sharper transformation peaks compared to the conventional cast alloy. Moreover, the suction cast NiTi alloy shows a significant improvement over the conventional cast one, in terms of possessing higher deformation recovery rates and displaying the increased compressive strength and damping capacity by 4% and 20%, respectively.

Microstructure and room temperature mechanical properties of NiAl–Cr(Mo)–(Hf, Dy) hypoeutectic alloy prepared by injection casting

The NiAl–Cr(Mo)–(Hf,Dy) hypoeutectic alloys were prepared by conventional casting and injection casting techniques respectively, and their microstructure and room temperature mechanical properties were investigated. The results reveal that with the addition of Hf and Dy, the Ni2AlHf Heusler phase and Ni5Dy phase form along the NiAl/Cr(Mo) phase boundaries in intercellular region. By the injection casting method, some Ni2AlHf Heusler phase and Ni5Dy phase transform into Hf and Dy solid solutions, respectively. Moreover, the microstructure of the alloy gets good optimization, which can be characterized by the fine interlamellar spacing, high proportion of eutectic cell area and homogeneously distributed fine Ni2AlHf, Ni5Dy, Hf solid solution and Dy solid solutions. Compared with conventional-cast alloy, the room temperature mechanical properties of injection-cast alloy are improved obviously.

Effect of Magnetohydrodynamical Stirring Method on Deformation Resistance of AlSi7Mg Aluminium Alloy

Most of the industry oriented research and development is based on conventional casting alloys Al-Si. This paper presents the results of deformation the hypoeutectic AlSi7Mg alloy used to manufacturing pistons for combustion engines. This is the material about high plasticity and corrosion resistance. For the research it was produced by semi-continuous casting process with magnetohydrodynamic stirring in crystalliser (MHD) and in conventional casting way. The results of deformation resistance of both materials have been described.

Microstructure and RRA treatment of LFEC 7075 aluminum alloy extruded bars

The microstructures after casting and extruding, the mechanical properties and electrical conductivity after RRA treatment of conventional DC casting and low frequency electromagnetic casting (LFEC) 7075 aluminum alloy were investigated. The results showed that finer grains which distributed more homogeneously was obtained in LFEC ingots compared with those conventional DC ingots. The extruded bars of LFEC alloy kept its fine grain features of original as-cast structure. In the RRA treatment, with the extension of second aging time, the tensile strength and hardness of alloy decreased, but the electrical conductivity increased. Meanwhile, as the second aging temperature raised, the phase change rate in precipitation also increased. Under the same conditions, extruded bars of LFEC alloy had better performance than that of conventional DC cast alloy. The optimum RRA heat treatment process was 120 °C/24 h+180 °C/30 min+120 °C/24 h. The LFEC extruded bars acquired tensile strength 676.64 MPa, hardness 198.18, and electrical conductivity 35.7% IACS respectively, which were higher than that in the T6 temper, indicating that a notable RRA response takes place in LFEC extruded bars, whose second-step retrogression time was 30 min, and it was suitable for mass production.

DEFORMATION BEHAVIOR AND MICROSTRUCTURE EVOLUTION OF 7050 ALUMINUM ALLOY DURING SEMI-SOLID STATE COMPRESSION PROCESS

The compression characters of the semi solid slurries are the key to semi solid processing such as semi-solid rolling which has high strain rates during the deformation.The deformation mechanism of semi-solid alloy can be understood well only after the relationship between stress and strain is obtained.Among many relevant research works done up to now,very few studies focus on the 7050 aluminum alloy.In order to study the sensibility of 7050 aluminum alloy to the strain rates,temperatures and reductions,the deformation behavior and microstructure evolution of 7050 aluminum alloy under different compression parameters were studied in this work.The grain coarsening of 7050 aluminum alloy prepared by the strain induced melt activation(SIMA) method during the isothermal heating process was studied firstly.Then the compression tests,within the semi-solid temperature range,on conventional cast alloy and semi-solid alloy were carried out respectively by using a Gleeble-3500 material thermo-simulation machine with the strain rates from 0.1 s~(-1) to 10 s~(-1). The relationship between stress and strain was analyzed subsequently.The synergistic effect between liquid and solid was analyzed in-depth as well.In addition,the differences of cracks propagation between conventional cast alloy and semi-solid state alloy during compression were discussed.Experimental results show that the stress of conventional cast alloy has a higher level than that of semi-solid alloy,which is 12 MPa higher at the peak position and 9 MPa higher during the stabilization stage. Reductions,deformation temperatures and strain rates during compression have remarkable effects on the microstructure evolution and the liquid phase distribution.The high reduction leads to the sharp deformation of the grain shape.The deformation has an obvious transition region in the middle which can be clearly seen that elongated grains have a deflection toward the edge.The lower the temperature, the smaller the liquid fraction is.This leads to recrystallization during the compression.The strain rates contribute to the flowing and distribution of liquid phase.The liquid phase transfers hardly when consisting with the solid phase under the high strain rate(10 s~(-1)),which results in a uniform deformation in different regions.Because of the remarkable differences in microstructures between conventional cast alloy and semi-solid alloy,the evolution of cracks propagation is also different,which corresponds to a solid-liquid separation mechanism and a mixed separation mechanism respectively. Semi-solid alloy has spherical crystals that can slide easily when comparing with conventional cast alloy with dendritic crystals.This makes a further explanation for the lower stress of the semi-solid alloy.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF LAVES PHASE STRENGTHENING NiAl BASE COMPOSITE FABRICATED BY RAPID SOLIDIFICATION

The Laves phase strengthening NiAl base composite was fabricated by conventionally casting and rapid solidification, and their microstructure and mechanical properties were investigated together. The results exhibit that the Laves phase in the conventional cast alloy is relative coarse and distributes along the NiAl phase boundary. Moreover, small stick–like Laves phase precipitates in the NiAl phase. Due to the segregation of Ni and Al in Laves phase, it still keeps the C14 crystal structure. The rapid solidification refines the NiAl and Laves phase greatly and promotes the formation of NiAl/Laves phase eutectic structure, which surrounds the NiAl phase and forms the cell–like structure. However, the rapid solidification can not handicap the precipitation of needle–like Laves phase in the NiAl phase. But, the rapid solidification restrains the formation of α–Cr phase. The compression * :k2u^MH hR` 2012CB933600, .:A 4f 1319 tests show that the cell–like Laves phase strengthening NiAl base composite has better mechanical properties at ambient and elevated temperature, compared with the conventional cast alloy. The improvement of mechanical properties should be attributed to the cell–like Laves phase and the nanocrystallization of the cell–like Laves phase during high–temperature deformation.

Microstructure and mechanical properties of conventional cast and rheocast Mg–Sn based alloys

In the present study, microstructure and mechanical properties of conventional cast and rheocast Mg–Sn alloy systems were investigated. The microstructure of conventional cast Mg-5%Sn and Mg-8%Sn alloys showed different phases, such as primary α-Mg, β-Mg2Sn phase that precipitates at the grain boundary, and eutectic α-Mg, a dark area surrounding the precipitate phase. With the addition of misch metal in Mg-5%Sn alloy the refinement of microstructure was observed and also the interdendritic second phase changed from rod/irregular shaped to rod and feathery shaped. In Mg-8%Sn-3%Al-1%Si alloy, α-Mg, Mg2Sn, Mg17Al12 and Mg2Si phases were observed. With the addition of Al–Sc master alloy in Mg-8%Sn alloy the matrix grain size became finer. The rheocast microstructures showed that the primary α-Mg phase is non-dendritic and globular shaped. Solution heat treatment at 520°C for 48–72h leads to complete dissolution of Mg2Sn intermetallic in Mg–Sn alloys. During ageing at 200°C discontinuous precipitates were formed at the grain boundaries in the initial stage and later continuous precipitates were occurred in the remaining regions. Hardness values were significantly improved after 100h of aging for all the alloys compared to as-cast alloys. The tensile properties of rheocast alloys were significantly higher than the conventional cast alloys.

Effect of mechanical conditions on the microstructures and mechanical properties of thixoformed Al–Cu–Si–Mg alloy

Commercial thixoforming is generally based on conventional aluminum-based casting alloys such as A356 and A357, which provide high fluidity and good castability. However, these alloys do not give such high mechanical properties as the alloys that are conventionally wrought such as Al–Cu–Si–Mg alloys, which generally has wide freezing ranges and tend to be prone to inhomogeneous microstructure and hot tearing. In this paper, one kind of aluminum alloy based on Al–Cu–Si–Mg system was thixoformed under different mechanical conditions. The strain induced melt activated (SIMA) route was used to obtain the semisolid slug for thixoforming. The effect of mechanical conditions on the microstructures and tensile mechanical properties in the T6 condition of the thixoformed aluminum alloy were studied. On proper mechanical condition (the base of component is 15mm), the thixoformed sample reveals a relatively homogeneous structure among different regions and presents no evidence of macro and microporosities, moreover, the tensile mechanical properties are uniform between the wall and the base. The ultimate tensile strength (376MPa) is close to the wrought target, and the elongation to fracture (18.7%) is even better, nevertheless, the yield strength (220MPa) is considerably short of the wrought value. On improper mechanical condition (the base of component is 5mm), the microstructures are inhomogeneous and inferior with respect to those of the former, and present some microporosities and microcracks. Although, a few cracks were filled by the supplied liquid metal, the mechanical properties are not satisfactory (tensile strength of 346MPa, yield strength of 216MPa and elongation to fracture of 11.5%).

Effect of Forming Process on Microstructure and Mechanical Properties of ZK60 Alloy Sheet

Abstract The microstructure and mechanical properties of ZK60 alloy sheet produced by different method were investigated using OM, SEM, TEM and a standard universal testing machine. The results show that, for conventional casting (CC) alloy, the equiaxed structure is refined after warm rolling. But for twin roll casting alloy, the microstructure changes from dendrite to fibrous deformed structure after warm rolling. Relatively higher density of shear bands can be observable in TRC ZK60 alloy sheet and no obvious dynamic recrystallization has been found after warm rolling. After warm rolling, the two alloys possess good mechanical properties, and the strength of TRC alloy is much higher than that of CC alloy, and elongation of TRC alloy is a little lower than that of CC alloy. The annealing heat treatment after warm rolling will induce a little decrease of strength and great increase of elongation of the two alloys. The tensile strength, yield strength and elongation of TRC and CC alloy sheet are 388 MPa, 301 MPa, 22.9%, and 311 MPa, 219 MPa, 19.3%, respectively. The grain refinement during manufacturing processes is attributed to the formation of heavy shear bands, high density dislocation, twins, and the recrystallization during subsequent annealing process.

Prediction of elastic properties of precipitation-hardened aluminum cast alloys

A methodology is proposed for predicting the elastic properties of precipitation-hardened alloys by combining different modeling techniques: the CALPHAD method, first-principles calculation, and elasticity models. The proposed procedure was applied to conventional aluminum cast alloys to predict their elastic moduli. The predicted Young’s moduli are in reasonable agreement with values reported in the literature, which verifies the potential applicability of the methodology to the development of high-stiffness aluminum cast alloys.

Effect of ultrasonic vibration during casting on microstructures and properties of 7050 aluminum alloy

The microstructures and properties of ultrasonic and conventional cast 7050 aluminum alloys have been studied. Compared with the conventional cast alloy, the ultrasonic cast ingot (UI) is characterized with a finer microstructure than that in the conventional cast ingot (CI). For the hot-rolled plates, the UI alloy can be aged faster and aging-strengthened easier than the CI alloy. When aged at 120 °C, the UI alloy reaches its peak strength after 8 h, with tensile strength of 602 MPa, yield strength of 547 MPa and elongation of 12.7%, respectively, whereas the CI alloy plate is with its tensile strength, yield strength and elongation of 536 MPa, 462 MPa and 15.0%, respectively, after peak aged for 12 h.

Study on Semi-Solid Magnesium Alloy Produced by Mechanical Stirring

Semi-solid magnesium alloy slurry was produced by a newly self-developed mechanical stirring machine in order to prepare continuous semi-solid slurry. The changing principle of semi-solid microstructure was studied under different conditions—the changing of temperature, stirring rate, cooling rate and stirring time. It was showed that the lower the temperature of slurry, the higher the stirring rate, the longer the stirring time and the faster the cooling rate, the grain will be smaller and more evenly rounded. When the stirring speed and temperature are the same, better semi-solid spherical grains can be gained by increasing the stirring time. At the same stirring temperature and higher stirring speed, semi-solid spherical particles are smaller, rounder and more evenly; at a low stirring speed, we can't get ideal semi-solid spherical grains even if we increase the stirring time. The ideal technological parameters of semi-solid AZ61 alloy produced with no-dendritic structure were recommended to be 600°C～605°C (stirring end temperature) 、3min～ 5min(stirring time) and 500r/min(stirring rate). Compared with conventional casting alloy, semi-solid alloy mechanical properties were greatly improved. The non-dendrite semi-solid forming mechanism was studied; mechanical stirring semi-solid non-dendritic formation was the result of a variety of factors, the key cause is mechanical shear stress.

Microstructure and mechanical properties of NiAl–Cr(Mo)–Hf/Ho near-eutectic alloy prepared by suction casting

Abstract The microstructure and mechanical properties of 0.15 at.% Hf and 0.2 at.% Ho doped Ni-33Al-28Cr-6Mo near-eutectic alloys prepared by conventional casting and suction casting were investigated. The results reveal that the addition of Hf and Ho results in the formation of Ni2AlHf and Ni2Al3Ho phases, respectively, along the NiAl and Cr(Mo) phase interface in intercellular regions. Compared with the conventional-cast alloy, the microstructure of suction-cast alloy is well optimized, characterized by the thin interlamellar spacing, high proportion of eutectic cell area and fine homogeneously distributed Ni2AlHf and Ni2Al3Ho phases. Furthermore, the room temperature mechanical properties of the suction-cast alloy improve significantly, which can be attributed to fine microstructure, uniform distribution of the Ni2AlHf and Ni2Al3Ho phases and solid solubility extension.

Microstructural evolution and tensile mechanical properties of thixoforged ZK60-Y magnesium alloys produced by two different routes

Semi-solid processing of magnesium alloys is generally based on conventional magnesium-based casting alloys such as Mg–Al series. However, these casting alloys do not give such high mechanical properties as the alloys that are conventionally wrought such as Mg–Zn series. In this paper, a ZK60 magnesium alloy with the addition of Y was thixoforged. The semi-solid thermal transformation (SSTT) route and the recrystallisation and partial melting (RAP) route were used to obtain the semi-solid feedstocks for thixoforging. Microstructural evolution during partial remelting was studied at temperatures for times. Tensile mechanical properties of thixoforged components at room temperature were examined. Results show that a fine spheroidal microstructure can be obtained by the RAP route. Compared to the RAP route, the SSTT alloy shows coarsened solid grains with a relatively high proportion of intragranular liquid droplets. With prolonged holding time, the solid grain sizes of the SSTT alloy and the RAP alloy increased. Coalescence was dominant in the SSTT alloy and Ostwald ripening was dominant in the RAP alloy. Thixoforging for the SSTT alloy and the RAP alloy resulted in successful filling of the die. The tensile properties of the thixoforged RAP alloy were satisfactory and exceeded those of the thixoforged SSTT alloy. However, the mechanical properties of both the thixoforged SSTT alloy and the thixoforged RAP alloy decreased with prolonged holding time.

In situ observation of solidification phenomena in Al–Cu and Fe–Si–Al alloys

Synchrotron radiation enables the observation of solidification in metallic alloys. In situ observations of solidification for Al–Cu alloys (5, 10 and 15 wt-%Cu) are reported. Nucleation and fragmentation of dendrite arms were often observed in the 15 and 10%Cu alloys when unidirectional solidification was performed from the planar interface. In contrast, nucleation and fragmentation were rarely observed in the 5%Cu alloys. The nucleation ahead of the solidifying front and the fragmentation in the mushy region strongly depended on alloy composition. This paper also presents in situ observation of solidification of Fe–10Si–0·5Al (at-%) alloys. The dendritic growth of δ-Fe was clearly observed using this technique. The development of X-ray imaging techniques enables the solidification of various conventional cast alloys such as Al, Ni and Fe alloys to be observed and will be increasingly used to investigate solidification phenomena.

Microstructure and mechanical properties of Hf and Ho doped NiAl–Cr(Mo) near eutectic alloy prepared by suction casting

The microstructure and mechanical properties of 0.15 at.% Hf and 0.2 at.% Ho doped Ni–33Al–28Cr–6Mo near eutectic alloys prepared by conventionally casting and suction casting were investigated. The results reveal that the addition of Hf and Ho results in the formation of HfAlNi 2 and HoNi 2Al 3 phases respectively along the NiAl and Cr(Mo) phase interface in intercellular regions. Compared with the conventional-cast alloy, the suction casting optimizes the microstructure of the alloy further, which can be characterized by the refined NiAl/Cr(Mo) eutectic lamellar, high proportion of eutectic cell, and fine and homogeneously distributed HfAlNi 2 and HoNi 2Al 3 phases. In addition, the compression tests show that the suction-cast alloy has better mechanical properties, which can be attributed to the fine microstructure and uniform distribution of the HfAlNi 2 and HoNi 2Al 3 phases.

High strain rate superplasticity of ultrafined Ti–10V–2Fe–3Al compact prepared by sintering and isothermal forging

High strain rate superplasticity was obtained for powder Ti–10V–2Fe–3Al (Ti-1023) alloy prepared by powder sintering and isothermal forging technology. The selected powder was cold isostatic pressed, sintered and isothermal forged to prepare this powder alloy. Tensile testing was conducted at optimum superplastic temperaure of 1023 K with different initial strain rate, and the elongation to failure, the flow stress and the microstructure were analysed. The experiment results exhibited that the microstructure of this powder alloy is extraordinary uniform and fine, resulted in considerable enhancement of optimum initial strain rate increased from 3·3×10−4 s−1 of conventional cast and wrought Ti-1023 alloy to 3·3×10−3 s−1 of this powder alloy. The elongation to failure increased first and then decreased with initial strain rate from 3·3×10−4 to 3·3×10−2 s−1. The strain rate sensitivity m is about 0·46 near initial strain rate of 3·3×10−3 s−1, larger than conventional cast and wrought Ti-1023 alloy. Microstructure observations showed that dynamic recrystallisation and grain growth were present during superplastic deforming.