Solidification and processing of aluminium based immiscible alloys

Copyright @ 2009 TMSThe Al-Sn and Al-Pb based immiscible alloys have significant potential for bearing applications. However, the mixing and understanding of solidification process for immiscible alloys have been long standing challenges for their development. This paper presents solidification and microstructural evolution of the Al-Sn-Cu alloys and also describes the mechanism of effective mixing by the intensive shearing. The experimental work was also focused on analyzing the effects of shear rate, temperature and time on Sn droplets size and their distribution. Results have been compared with earlier study on Al-Si-Pb alloys. Experimental results suggest that the intensive shearing process produces homogeneous and finely dispersed Sn and Pb droplets.This work was funded by the EPSRC and DTI

Remote laser welding of Zn coated IF steel and 1050 aluminium alloy: processing, microstructure and mechanical properties

The integrity of steel-aluminium dissimilar alloy joints is dependent on the intermetallic phases (IMCs) and the extent of the bonding area. The excessive growth of brittle AlxFexIMCs within the weld pool and interfaces is disadvantageous due to the initiation and propagation of hot and cold cracking during the solidification. The purpose of this work was to assess the development of Remote Laser Welded (RLW) joints of Zn coated interstitial free (IF) steel to 1050 aluminium alloy, which can be used in cooling circuits and electrical connectors in automotive applications. Welding experiments with variable RLW parameters (power, welding speed and focal offset) were performed to study the formation of IMCs and impact of joint integrity. Results showed that while in conduction mode (at power densities of 0.13-0.18 MW/cm2) three IMCs were identified through SEM/EDX and EBSD: η - Al5Fe2, κ - AlFe3and θ - Al13Fe4which possessed nano-hardness indentation values of approximately 12, 5 and 5 GPa, respectively; they formed in a non-continuous interfacial layer, the weld pool composition remained homogenous, and cracking was minimal. On the contrary, in keyhole mode (at power densities of 0.16-0.40 MW/cm2) welded samples produced a continuous and thick IMC layer, continuous and/or excessive cracking and an inhomogeneous weld pool composition due to the excessive mixing of steel and aluminium, of up to 10 wt.% of Al in the weld pool. The nominal lap shear strength for the sample produced in conduction mode was of 77%, with respect to the weakest joint material (Al). This work found a close link between the welding mode and weld pool chemistry which significantly determined the IMCs distribution and thickness, extent of cracking within the weld pool and mechanical properties

Superplastic forming characteristics of AZ41 magnesium alloy

An AZ41 magnesium alloy in the hot-rolled condition without further thermomechanical processing to modify its microstructure was investigated to establish its suitability for use within a superplastic forming process and to establish optimum forming parameters. Formability was assessed using elevated temperature tensile testing and hot gas bulging, across a range of strain rates (1×10−1−1×10−3 s−1) and temperatures (350−450 °C). Circle grid analysis with GOM Aramis cameras was used to understand peak strains and material thinning in relation to industrial forming processes. Post forming EBSD and STEM analysis was conducted to understand the mechanisms responsible for the materials formability, with dynamic recrystallization being clearly evident. Peak elongation of 520% was achieved at 450 °C and 1×10−3 s−1; industrially relevant elongation was achieved at 1×10−2 s−1 at both 450 °C (195%) and 400 °C (170%)

Understanding the corrosion behaviour of Al-Mg alloy fabricated using a Laser Powder Bed Fusion (L-PBF) Additive Manufacturing (AM) process

Metal additive manufacturing (AM) is an emerging disruptive technology capable of manufacturing complex shaped components that are difficult to manufacture through conventional methods. However, the corrosion behaviour of AM fabricated parts must be considered for safety critical applications. For this reason, we have studied the relationship between AM fabricated Scalmalloy (Al-Mg-Sc-Zr) microstructures and their corresponding corrosion behaviours. This comparison has been drawn against a comparable commercial Al-Mg alloy (5182). The corrosion resistance of the samples in salt water was assessed via various electrochemical analytics techniques. It was observed that Scalmalloy produced better corrosion resistance than 5182 Al-alloy. This can be attributed to the spontaneous formation of a passive film on refined AM microstructure and the presence of Sc and Zr, specifically when samples were fabricated with higher density (less porosity). The alloys’ corrosion mechanisms were dependent on immersion time and the microstructural features of the samples

Effects of the adjustable ring-mode laser on intermetallic formation and mechanical properties of steel to aluminium laser welded lap joints

Research has confirmed a positive effect of laser beam shaping on controlling weld profiles and keyhole stabilisation, with significant reductions of porosity in weldments. However, few attempts with scattered results have studied the impact of laser beam shaping on intermetallic phase formation. This paper implements the adjustable-ring mode (ARM) laser and studies the impact of the core/ring power ratio to explore the impact on intermetallic phase formation and mechanical properties during remote laser welding of IF steel to 1050 aluminium. It was found that in conduction mode, the core/ring power ratio of 0.2 provided a larger surface area for bonding at the weld interface, and this was translated through the maximum lap-shear strength of 97.6 N/mm2 (joint efficiency 71%). Furthermore, this significantly reduced the Fe2Al5 intermetallic compound (IMC) thickness by 62% and total IMC thickness by 40% in contrast to a core-dominant beam (power ratio greater than one). In keyhole mode, cracking and lower lap-shear strengths were observed compared to the conduction mode. Notably, with a core/ring power ratio of 0.5 a significant grain refinement in the steel side of the weld was observed

Scan strategy induced microstructure and consolidation variation in the laser-powder bed fusion (L-PBF) additive manufacturing of low alloy 20MnCr5 steel

Data availability: Data will be made available on request.Copyright © 2023 The Author(s). The paper focuses on the effect of the scanning strategies on the microstructural evolution, defect formation, and macro-hardness performance of laser-powder bed fusion (L-PBF) produced samples of low alloy 20MnCr5 steel. Respect to the scanning strategies, advanced characterization techniques were employed to study (i) as-built microstructure, (ii) inclusion size and distribution, and (iii) details of compositional variation around porosity and within the build. Microstructural characterization shows that the chessboard scanning strategy can provide a favorable microstructure for the improvement of mechanical performance. However, macro-hardness results show a lower mechanical performance compared to the linear scanning strategy samples, which is contradicted by the improved microstructure. Experimental results reveal that the chessboard scanning strategy promotes the oxidation reaction and in-situ oxide (SiO2) formation in L-PBF, which leads to significant defect formation due to the excessive thermal profile from the overlap of the laser. This has been validated through finite element analysis and thermodynamic computation. The advantages of microstructural improvement using the chessboard strategy can only be realized with strict control of the metallurgical quality during the L-PBF process. Thermal profile optimization and oxygen elimination during the L-PBF process could be critical for the improved metallurgical quality and superior mechanical performance of the as-built components.XY and ZL would like to thank the financial supported from EPSRC grant (EP/N011368/1). HK would like to thank the financial supported by WMG Centre High Value Manufacturing Catapult and Liverpool John Moore University, Faculty of Engineering and Technology (FET) Pump Prime Awards 2022/23. The X-Ray Computed Tomography (XCT) work supported through the EPSRC Project Numbers (EP/T02593X/1 and EP/S010076/1)

Scan strategy induced microstructure and consolidation variation in the laser-powder bed fusion (L-PBF) additive manufacturing of low alloy 20MnCr5 steel

The paper focuses on the effect of the scanning strategies on the microstructural evolution, defect formation, and macro-hardness performance of laser-powder bed fusion (L-PBF) produced samples of low alloy 20MnCr5 steel. Respect to the scanning strategies, advanced characterization techniques were employed to study (i) as-built microstructure, (ii) inclusion size and distribution, and (iii) details of compositional variation around porosity and within the build. Microstructural characterization shows that the chessboard scanning strategy can provide a favorable microstructure for the improvement of mechanical performance. However, macro-hardness results show a lower mechanical performance compared to the linear scanning strategy samples, which is contradicted by the improved microstructure. Experimental results reveal that the chessboard scanning strategy promotes the oxidation reaction and in-situ oxide (SiO2) formation in L-PBF, which leads to significant defect formation due to the excessive thermal profile from the overlap of the laser. This has been validated through finite element analysis and thermodynamic computation. The advantages of microstructural improvement using the chessboard strategy can only be realized with strict control of the metallurgical quality during the L-PBF process. Thermal profile optimization and oxygen elimination during the L-PBF process could be critical for the improved metallurgical quality and superior mechanical performance of the as-built components

Effect of a ring-shaped laser beam on the weldability of aluminum-to-hilumin for battery tab connectors

Advances in laser beam shaping technologies are being studied and are considered beneficial in many aspects of dissimilar metal joining, which include reducing intermetallic compounds (IMCs), optimizing weld pool profiles, and controlling porosity and spatters. This paper utilizes a coaxial ring and core dual beam laser and aims to study the impact of the power ratios between core and ring beams on the weldability of 1100 aluminum alloy to hilumin (steel). High-resolution electron microscopy was performed in the cross sections of the weld pools to quantify the melt pool composition and subsequent IMC formation and weld defects (cracking and cavitation). Lap-shear mechanical testing and electrical resistivity testing were also carried out. Results showed that the optimal power ratio for lap-shear strength was 0.4 (intermediate core and ring) due to the reduction in the Fe-rich liquid into the upper weld region. As a result, this produced a smaller interface between the Fe-rich region and Al, thus reducing the formation of the most detrimental IMC (e.g., Fe2Al5). Conversely, a power ratio of 0.2 (core-dominant) was found beneficial for reducing electrical resistance due to a reduced total IMC volume

Grain refinement of Al-Si hypoeutectic alloys by Al3Ti1B master alloy and ultrasonic treatment

Al-Si alloys are widely used in automotive and aerospace industries due to their excellent castability, high strength to weight ratio and good corrosion resistance. However, Si poisoning severely limits the degree of grain refinement with the grain size becoming larger as the Si content increases. Generally the effect of Si poisoning is reduced by increasing the amount of master alloy added to the melt during casting. However, an alternative approach is physical grain refinement through the application of an external force (e.g. mechanical or electromagnetic stirring, intensive shearing and ultrasonic irradiation). This work compares the grain refining efficiency of three approaches to the grain refinement of a range of hypoeutectic Al-Si alloys by (i) the addition of Al3Ti1B master alloy, (ii) the application of Ultrasonic Treatment (UT) and (iii) the combined addition of A13Ti1B master alloy and the application of UT

Effect of the electrical discharge machining on Ti6Al4V corrosion behaviour in simulated body fluid

Titanium alloys, such as Ti6Al4V, are widely employed in the biomedical industry for implant applications due to their favourable properties. However, these alloys can experience long-term corrosion in the presence of bodily fluids, which is a critical concern for implants as it affects their timespan. Therefore, this study aimed to examine the corrosion resistance of Ti6Al4V in body fluid. Highly desirable electrical discharge machining (EDM) techniques used for Ti6Al4V sample preparation with three different conditions (oil, deionized water, and hydroxyapatite mixed in deionized water). Corrosion was assessed using electrochemical analyses, with microstructural analysis. Results indicated that the samples produced using water and oil had the best and lowest corrosion resistance, respectively. Protective oxide layer formed during the EDM in water while heterogeneous surface was produced for EDM in oil. The increase in capacitance leads to the thickening of the oxide layer, thereby enhancing the corrosion resistance