Cast Alloy Research Articles

METHODOLOGY AND EQUIPMENT FOR RESEARCHING CORROSION CRACKING PROCESSES IN CASTING ALLOYS

Corrosion cracking is the destruction of metal under static stresses and an aggressive environment. Corrosion fatigue is destruction of the metals and the alloys under the impact of cyclic mechanical pressure and aggressive environment simultaneously.Stress corrosion is the least studied and systematized in terms of literature data on the impact of various aggressive environment (type, temperature, and concentration), composition and structure of the material, mode of heat treatment, method of obtaining and cleaning the casting, methodology for determination of corrosion under stress, as well as equipment for carrying out similar studies. The purpose of this paper is to present the methodology and equipment developed for corrosion cracking testing of cast alloys.

Effects of Superheating Treatment on the Microstructure, Tensile and Thermal Conductivity Properties of Fe-Bearing Al-10Si-Mg Casting Alloy

In this study, we designed and manufactured a new Fe-bearing Al-10Si-Mg casting alloy (F alloy) and investigated its microstructure, mechanical properties, and thermal conductivity. Two types of Fe-bearing Al-10Si-Mg alloys were used: the Conventional-F alloy, injected at 720 ℃ and cooled by water quenching, and the Superheated-F alloy, heated to 820 ℃ and maintained at that temperature for 1 hour. Subsequently, it underwent a degassing process at 720 ℃ before being cooled by water quenching. Both the Conventional-F alloy and the Superheated-F alloy exhibited dendritic microstructures and Fe-intermetallic compounds. The Secondary Dendrite Arm Spacing (SDAS) of the Conventional-F alloy measured 32.4 μm, whereas the Superheated-F alloy measured 28.6 μm. Additionally, the average eutectic Si sizes were 10.3 μm for the Conventional-F alloy and 7.7 μm for the Superheated-F alloy. Fe-rich IMCs were observed in the eutectic region, with their size decreasing due to the superheating treatment. Tensile tests at room temperature were conducted at a strain rate of 10<sup>-3</sup>/s. The Conventional-F alloy exhibited a yield strength (YS) of 93.4 MPa, ultimate tensile strength (UTS) of 183 MPa, and an elongation (El.) of 6.4%. Conversely, the Superheated-F alloy displayed a YS of 115.4 MPa, UTS of 218.2 MPa, and an El. of 5.1%. The mechanical properties notably improved with the superheating treatment. Regarding thermal conductivity, the Conventional-F alloy exhibited 114.9 W/m·K, while the Superheated-F alloy displayed 153.7 W/m·K. This represents a roughly 14% increase compared to the thermal conductivity of the commercial Al-10Si-Mg material (Silafont36: 135.1 W/m·K). The effects of the Superheating Treatment on microstructural characteristics, deformation behavior, and thermal conductivity of the Fe-bearing Al-10Si-Mg casting alloys were discussed.

Processing and characterization of beryllium free Ni–Cr–Mo biomaterial doped with cerium, boron and titanium for dental applications

Dental restoration has been a major concern of healthcare since centuries. Several alloys are in use for dental prostheses including Ni–Cr–Mo alloy. The Ni–Cr–Mo alloy has advantage of economy and density over other alloys, while possessing equivalent corrosion and biocompatibility characteristics. However, beryllium in Ni–Cr–Mo dental casting alloys has associated health hazards, being carcinogenic. In this research Ni–Cr–Mo alloys with minor additions of boron (0.2 wt %), cerium (0.4 wt %) and titanium (2 wt %), to replace beryllium were developed through vacuum induction melting and investment casting technique. Manufacturing steps are detailed for the alloy development to have medically clean alloy, suitable for biomedical applications. The cast alloy samples were tested for microstructure, phases, melting temperatures, wear and corrosion characteristics. Corrosion and wear test results demonstrate that the composition with minor addition of cerium had a significant effect to have low corrosion rate (25.92 × 10−3 mills per year), low wear rate (0.04 × 10−4 mm3/N.m) and lowest coefficient of friction.

Investigation of segregation behaviour in 2060 aluminium-lithium alloy during twin-roll casting

The utilization of the twin-roll casting process to fabricate aluminium (Al) - lithium (Li) alloys is regarded as an efficient and energy-saving strategy to meet the aerospace industry’s demands for reducing processing steps, cost-effectiveness, and corrosion resistance. This study successfully achieved the preparation of Al-Li alloy twin-roll cast slabs across various processing ranges to investigate the corrosion resistance differences in different processing conditions. Remarkable macro segregation phenomena were observed in the fabrication under high twin-roll casting speeds for TRC-3. By combining temperature and flow rate calculations, we comprehensively analysed the results of this segregation mechanism. The segregation is inherited into the final T6 state microstructure, exacerbating the precipitation of the T1 phases and deteriorating the ultimate corrosion resistance performance. We delved into a profound discussion regarding the mechanistic impact of segregation on corrosion behaviour. Ultimately, this study postulates a process parameter range for twin-roll casting of Al-Li alloys, aimed at attaining minimal segregation and maximal corrosion resistance.

The influence of additive manufacturing on Portevin-Le Châtelier (PLC) effect in Ni–Co-based superalloy

The microstructures and tensile properties of the Ni–Co-based superalloys made by additive manufacturing (AM) were investigated. The results revealed that both normal and inverse Portevin-Le Châtelier (PLC) effects were observed in AM Ni–Co-based superalloys. In addition, AM significantly inhibited the PLC effect, the average stress decrements for the cast and wrought (C&W) alloys with the same nominal compositions were more than ten times as large as those for the AM alloys when tested at 400 °C with a strain rate of 3 × 10−4 s−1. In the AM Ni–Co-based superalloys, type C serrations had connections with the inverse PLC effect. Transmission electron microscope (TEM) was performed to investigate the interactions of solute atoms, dislocations, stacking faults (SFs) and the γ′ phase for a deep insight into mechanisms of the PLC effects and clarifying the changes in serration types and the conversion from normal to inverse PLC effect.

Effect of Cu on Solidification Microstructure and Solidification Process in High Carbon High Speed Steel Type Cast Alloy

Effect of Cu on Solidification Microstructure and Solidification Process in High Carbon High Speed Steel Type Cast Alloy

Strip Casting of Sm2TM17-Type Alloys for Production of the Metastable SmTM7 Phase

Conventional book casting of Sm2TM17-type alloys (where TM = Co, Fe, Cu, Zr) leads to a coarse, highly segregated microstructure, predominantly due to the slow, variable cooling rate from the mould surface towards the centre of the ingot. These cast alloys require a long homogenisation treatment to remove this segregation and develop a super-saturated, metastable SmTM7-type hexagonal phase. This SmTM7 phase is a vital precursor phase required during magnet production to develop the complex cellular structure responsible for high magnetic properties. In this work, strip casting was employed to facilitate rapid solidification to develop thin flakes (<0.5 mm thick) with a columnar grain structure. Rapid cooling has the potential to produce a homogenous microstructure consisting predominantly of the metastable SmTM7 phase. This could remove or significantly reduce the need for the energy-intensive homogenisation treatment usually required in conventional magnet manufacture. This paper investigates the effect of wheel speed (and hence cooling rate) on flake thickness, microstructure, and phase balance of the cast alloys. It was shown that for wheel speeds between 1.1 and 3.0 m/s, the microstructure showed large variation; however, in all cases, evidence of the columnar SmTM7 phase was presented. The adhesion between the melt and the wheel was deemed to be critical for the nucleation and subsequent columnar growth of SmTM7 grains, where the wheel speed controlled both the flow of the alloy onto the wheel and the thickness of the resultant flake. It was determined that in order to achieve a homogenous columnar SmTM7 structure, the maximum flake thickness should be limited to 270 μm to avoid the formation of equiaxed Sm2TM17 grains through insufficient cooling.

Thermomechanical fatigue behavior and its life prediction of AlSi9Cu3.5 cast alloy

Thermomechanical fatigue behavior and its life prediction of AlSi9Cu3.5 cast alloy

Research on Fe Removal, Regeneration Process, and Mechanical Properties of Mg Alloy AM50A

In recent years, the widespread application of Mg alloy casting and Mg alloy products has generated a large amount of Mg alloy waste. This experiment used a single factor experimental analysis method to study the optimal process for removing Fe from Mg alloy AM50A waste, and developed an efficient Fe removal and regeneration process for Mg alloy AM50A. It was found that the optimal refining temperature for removing Fe ions was 670 °C, the optimal refining (RJ-2) agent mass ratio was 1.5%, and the optimal refining time was 40 min. Regenerated J40-1.5-AM50A Mg alloy was prepared using the best refining process, and its composition and mechanical properties were tested and analyzed. The experimental results show that the composition of the regenerated J40-1.5-AM50A Mg alloy prepared by this method is consistent with AM50A, with an Fe removal rate of 96.2%. The mechanical properties were improved compared to the original AM50A sample, with a maximum tensile strength increase of 1.611 KN and a tensile strength increase of 26.333 MPa. The elongation after fracture is 2.25 times that of the original sample. Research has shown that the RJ-2 refining agent can provide mechanical properties of magnesium alloys during the refining process. By analyzing the composition, XRD, SEM, and EDS of AM50A (Fe) and J40-1.5-AM50A, it was found that the refining process accelerates the removal of Fe in the form of Fe deposition.

Diamond machining of additively manufactured Ti6Al4V ELI: Newer mode of material removal challenging the current simulation tools

Single point diamond machining (SPDM) produces smooth machined surfaces that other production methods cannot match. While the mechanics of machining of cast alloys with SPDM is well-explored, the realm of SPDM for additively manufactured parts remains largely uncharted. This work reveals new insights into the surface generation process of an additively manufactured titanium alloy, specifically, a Ti6Al4V Extra Low Interstitials (ELI) alloy workpiece. Our examination of the chip morphology unveiled a distinct mode of chip removal, previously unrecorded in existing literature. During SPDM of additively made Ti6Al4V ELI workpiece, identification of numerous pores and discontinuities in the chips flowing on the tool rake face, indicating periodic intermittent cracking during the material's plastic flow was seen. To examine this phenomenon, a finite element analysis (FEA) model was developed. While the FEA model can well explain the machining mechanics and chip morphology of SPDM of cast Ti6Al4V ELI reported in the literature, it failed to describe the chip morphology that are obtained during machining of additively made workpiece in this work. This disparity underscores the need for innovative simulation approaches tailored for additively manufactured components. The experimental observations in this study highlight a unique form of chip formation in contrast to conventional Ti6Al4V alloy machining processes. At lower feeds, there was a presence of short, discontinuous chip formation with tearing at the outer periphery. Conversely, at higher feeds, a long, continuous ribbon-like chip formation was observed. In addition, some typical additive manufacturing defects appear on the machined surface and chips. Through optimisation of the SPDT parameters, a surface roughness (Ra) value of about 11.8 nm was achieved on additively manufactured Ti6Al4V ELI workpiece. This work provides a fresh perspective on the mechanics of SPDM for additively manufactured components, offering a stepping stone for subsequent studies.

The influence of rolling on the corrosion and wear resistance of the MAO coating on ZM5 alloy

PurposeThe impact of rolling on the performance of micro arc oxidation (MAO) coatings on ZM5 alloy has been underreported. The purpose of this study is to explore the correlation between rolling and the failure mechanism of MAO coatings in greater depth.Design/methodology/approachThe influence of rolling on the corrosion and wear properties of MAO coating was investigated by phase structure, bond strength test (initial bond strength and wet adhesion), electrochemical impedance spectroscopy and wear test. The change of the surface electrochemical properties was studied by first principles analysis.FindingsThe results showed that the MAO coating on rolled alloy had better corrosion and wear resistance compared to cast alloy, although the structure and component content of two kinds of MAO coating are nearly identical. The difference in interface bonding between MAO coating and Mg substrate is the primary factor contributing to the disparity in performance between the two types of samples. Finally, the impact of the rolling process on MAO coating properties is explained through first-principle calculation.Originality/valueA comprehensive explanation of the impact of the rolling process on MAO coating properties will provide substantial support for enhancing the application of Mg alloy anticorrosion.Graphical abstract

Influence of tool geometry on mechanical and microstructural characteristics of friction stir welded cast alloys

Abstract Cast alloys find suitable applicability in aerospace sector owing to low porosity, high specific strength, corrosion resistance, fluidity and good machinability. The investigation focuses on friction stir welding (FSW) of cast A356 and A2014 alloys with varied range of process parameters, namely tool pin shape (cylinder, threaded cylinder, square, and conical), tool rotation speed (1800–2100 rpm) and welding speed (10–25 mm × min−1). Experimentation on stirwelding was performed based on selected tool pin shape between varied tool rotation and welding speed. The output responses, namely Ultimate tensile strength (UTS) and micro hardness, have been evaluated to study the effect of each tool. The microstructural characteristics of the weld samples were analyzed using optical microscope and scanning electron microscope (SEM) technique. The microstructural observation unveiled that complete fusion prevails between the parent alloys devoid of micro porosities and segregations. The re-crystallization effect resulted in the finer grains. The cylinder-shaped tool with a thread and square shaped tool rendered better strength and hardness properties of 136.6 MPa and 109.4 HV, respectively.

ДОСЛІДЖЕННЯ ЩІЛЬНОСТІ МАКРОСТРУКТУРИ ВИЛИВКІВ ІЗ ВТОРИННОГО СПЛАВУ СИСТЕМИ AL-SI ПРИ МОДИФІКУВАННІ ВИСОКОДИСПЕРСНИМ КАРБІДОМ КРЕМНІЮ

The study analyzes the impact of modifying a secondary aluminum casting alloy of the Al-Si system with high-dispersion silicon carbide on the density of the metal and the macrostructure of cylindrical castings. It was found that the solidification rate and the structure of the metal depend on the type of mold (metal or sand-clay) and the amount of added SiC. Alloys with a 0.1% SiC addition, cast in a metal mold, have the highest density. The macrostructure of SiC-modified castings is characterized by the presence of deep shrinkage cavities and concentrated porosity. Castings poured into a sand-clay mold with SiC modification show concentrated shrinkage and gas pores, which corresponds to a low grade on the reference scale. The study highlights the importance of choosing the casting method and alloy modification to optimize the density and structure of the castings.

Barley Malt as a Binder for Moulding Sands—Gas Evolution and Surface Quality of Iron Castings

The requirements placed on the foundry industry are mainly related to the need to maintain an appropriate quality–price ratio of the product and to maintain an appropriate production regime that takes into account modern legal solutions related to environmental protection. This work is part of the trend of searching for new or previously unused materials from renewable sources in moulding sand technology. This article concerns the possibility of using barley malt in moulding material technology as a binding material. The presented work contains the results of research on the release of gases during casting, where high temperatures cause the decomposition of chemical substances. The tests confirmed that moulding sands with barley malt as a binder do not cause excessive emissions of harmful gaseous products when pouring moulds with liquid casting alloy. The volume of gases formed was smaller than that of commonly used moulding sands with other binders. The total volume of gases produced and the kinetics of their release indicate that casting in this type of moulding sand did not cause any technological inconvenience or casting defects of gaseous origin. This was confirmed by research involving obtaining iron castings in industrial conditions using barley malt as a binder in moulding sand technology, which were then subjected to visual assessment and roughness analysis.

Microstructural evolution and its influence on the wear resistance of a laser directed energy deposited Ni-based single crystal superalloy

The wear behavior of Ni-based single crystal (NBSC) superalloy SRR99 fabricated by laser-directed energy deposition (LDED) is investigated and compared with that of its cast counterpart. While γ’ precipitate size in the latter is > 400 nm, that in the former is an order of magnitude lower. Dry sliding wear tests reveal that the wear rate and coefficient of friction of the LDED alloy are 75 % and 20 % lower than that of its cast counterpart, respectively. Detailed transmission electron microscopy investigation of the wear-tested cast alloy indicates that there is orientation change and formation of nanoscale grains only at the top layer of the worn surface, whereas regions below undergo moderate plastic deformation via dislocation slip. In contrast, the sub-surface of the worn LDED alloy has a graded microstructure, with a composite of NiO/γ-Ni on the top, γ’ free nano-grains in the middle, and a highly deformed nanoscale layer at the bottom. The improved wear behavior of the LDED alloy is attributed to its higher dislocation density, finer γ’ precipitates, and the formation of this graded microstructure. Finally, a detailed description of mechanisms that lead to the formation of this unique graded microstructure is provided.

Comparison of microstructure, damping capacity, and mechanical properties of cast and deformation processed Fe17Mn alloys

There were few works on cast FeMn damping alloys although many studies have been conducted on deformation processed (DP) counterparts. In this study, we investigated the differences in damping and mechanical properties of as-cast and as-DP Fe17Mn alloys and the effect of solution treatment at 1050℃ (ST) on their properties. The as-cast Fe17Mn alloy demonstrated a higher damping capacity but lower strength than the as-DP Fe17Mn counterpart. As much as 18 % of the BCC phase was distributed as dendrite in the Mn-depleted region of the as-cast Fe17Mn alloy. The DP Fe17Mn alloy inherited some BCC phase with less than 1 % content formed during the casting. The ST further improved the damping capacity and plasticity but decreased the strength in both the cast and DP Fe17Mn alloys. After the ST, the cast Fe17Mn alloy also showed good mechanical properties, with tensile strength up to 645 MPa and fracture up to 40 %. Our results shed light on the potential application of cast Fe17Mn alloy in mechanical components.

Laser remelting of a novel carbide-reinforced Ni-Co-Cr-Hf-C alloy with ultra-fine HfC dispersion

The dispersion of stable nano-particles is essential for improving the high temperature creep properties of Ni-base alloys. Additive manufacturing by laser powder bed fusion (LPBF) offers novel means to tailor particle distributions taking advantage of the fast and directional solidification inside travelling melt pools. To benefit of this opportunity, a novel in-situ carbide reinforced alloy Ni − 32Co − 28Cr − 3.5Hf − 0.25C (wt. %) was developed. In a first rapid approach laser remelting of a cast alloy block was used to mimic LPBF solidification conditions. After a subsequent annealing treatment at 1150 °C for 6 h, an ultra-fine and intragranular dispersion of nano-sized HfC particles was obtained. The HfC particles have an average size of 54 nm and a mean inter-particle distance of 326 nm, which is an exceptional refinement compared to the as-cast microstructure. The number density of HfC particles ranges around 1 × 1012/m2 in 2D and is estimated to be 2 × 1019/m3 in 3D.

The role of the preparation route on microstructure and mechanical properties of AlCoCrFeNi high entropy alloy

Nearly equiatomic AlCoCrFeNi alloy samples were prepared by induction melting and mechanical alloying (MA) combined with spark plasma sintering (SPS). The cast sample showed a dendritic microstructure composed of spinodally decomposed nanometric constituents of the B2 and BCC phases. The spark plasma sintered sample exhibited an ultrafine-grained microstructure of B2 phase and FCC solid solution and Cr23C6 carbides. The MA + SPS sample was strengthened by compressive stress-strain test up to a yield strength of 2029 ± 5 MPa, resulting significantly higher compared to 1366 ± 32 MPa of the cast sample. In addition to the higher compressive yield strength, the sintered sample exhibited a hardness of more than 130 HV higher compared to the cast alloy. On the other hand, the cast alloy showed high plastic deformation (29%) and significantly high ultimate compressive strength of 3072 ± 122 MPa. Together with these mechanical characteristics, the MA + SPS sample showed good thermal stability while preserving the mechanical properties even after annealing at 800 °C. This was not the case with the cast sample, in which ductility and ultimate strength significantly decreased upon annealing at 800 °C. A substantial yield strength reduction of both MA + SPS and cast samples was recorded when tested at 800 °C. Nevertheless, stress-strain curve trends were observed to be quite different between the two samples, thus suggesting dissimilar deformation mechanisms under high-temperature compression.

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.

Insights into the effects of Sm on microstructure evolution mechanism and mechanical properties of Mg-8Gd-2Y–1Zn-0.5Zr cast alloy at high temperature

In this study, the effects of 1 % Samarium (Sm) on the microstructure and room and high temperature mechanical properties of Mg-8Gd-2Y–1Zn-0.5Zr alloy are discussed and analyzed. The addition of Sm increases the volume fraction of lamellar and blocky long-period stacking ordered (LPSO) phases and promotes the precipitation of lamellar β′ and β phases. The high yield strength and ultimate tensile strength of Mg-8Gd-2Y-1Sm-1Zn-0.5Zr alloy at room and high temperatures are mainly attributed to the strengthening effects of LPSO, β, and β′ phases. The LPSO, β, and β′ phases effectively hinder the movement of dislocations and inhabit the migration of grain boundaries. The Mg-8Gd-2Y-1Sm-1Zn-0.5Zr alloy shows superior yield strength (203.3 MPa) and ultimate tensile strength (258.9 MPa) at 350 °C, which are respectively 67.2 MPa and 23.8 MPa higher than those of Mg-8Gd-2Y–1Zn-0.5Zr alloy (136.1 MPa and 235.1 MPa).