Solidification Defects Research Articles

Controlling Ag3Sn Plate Formation and Its Effect on the Creep Resistance of Sn–3.0Ag–0.7Cu Lead-Free Solder by Adding Minor Alloying Elements Fe, Co, Te and Bi

Preventing the formation of large platelets of Ag3Sn intermetallic compounds (IMCs) during solidification of solder joints has become a significant challenge in the design of Sn–Ag–Cu lead-free solder alloys. Large platelets of Ag3Sn are generally considered as undesirable as their presence can create solidification defects and causes mechanical property anisotropy. In the present work, the synergetic effects of adding 0.1 wt% of Fe, Co, Te and 2 wt% Bi to Sn–3.0Ag–0.7Cu (SAC 307) solder are studied in terms of the growth of large platelets Ag3Sn IMCs and the resulting alloy’ creep resistance as well as their thermal behavior. Although minor Fe, Co, Te and Bi alloying elements addition causes large increase in the degree of undercooling from 3.4 to 22.3 °C with maintaining the pasty range and melting temperature at the same levels, the modified SAC307–FeTeCoBi alloy exhibits considerable increase in creep resistance (~ 10 times) and large fracture life-time than SAC (307) solder at same stress levels and testing temperatures. This is attributed to the transition of Ag3Sn IMCs from large platelets into fine needle-like morphology and formation of new (Cu,Co)6Sn5, FeSn2, SnTe IMCs and Bi particles, which could provide more obstacles for dislocation movement at the interphase boundaries.

Numerical Simulation of Solidification Structure of Continuously Cast Billet with Grain Motion

The motion of free grains has a significant influence on the solidification structure, solute distribution, and defects of large casts. However, few studies have modeled the solidification structure of large casts considering grain motion. In this paper, taking into account the motion of free grains, a multiscale cellular automaton model is proposed to predict the solidification structure of continuously cast billets. The model is validated with experimental measurements. Then, the proposed model is adopted to investigate the solidification structure evolution of a wire steel 82b cast by a bow-type continuous caster with a billet section size of 160 mm × 160 mm. The results show that the growth of columnar grains in inner arc of billet strand is promoted by the sedimentation of free equiaxed grains. But the columnar grains in outer arc of strand are blocked once free grains nucleate before them. Thus, asymmetric morphology of solidification structure in the 82b billet with casting speed of 1.8 m/min is quantitatively determined and the length of the columnar grains in the inner arc and the outer arc of strand is 57.0 mm and 31.0 mm, respectively. Moreover, compared with the difference of cooling intensity between inner arc and outer arc in secondary cooling zone, the motion of free grains dominates the asymmetric morphology in the 82b billet.

Effect of adding Ce on the hot-tearing susceptibility of the 5TiB2/Al-5Cu composite

Hot tearing is a severe solidification defect that occurs during the metal solidification process. To reduce the hot-tearing susceptibility (HTS) of a 5TiB2/Al-5Cu composite, rare-earth Ce with mass fractions of 0.2%, 0.5%, and 1% was added to the composite in this study. The results indicated that the HTS of the composite decreased with the increase of Ce from 0.2% to 1%. The HTS value of the 5TiB2/Al-5Cu composite decreased from 15.61 to 5.60, and the solidification-temperature range of the composites gradually narrowed after the Ce addition. In addition, the grain size of the composite was refined, and the average grain diameter decreased from 26.29 μm to 18.97 μm. With the increase in Ce content, the composite microstructure was refined and the TiB2 particle agglomeration dissolved. As the Ce increased, the finer lamellar Al8Cu4Ce phase promoted a more uniform microstructure and a more fluid liquid metal. Therefore, the residual liquid metal better fed the cracks, and the grain-boundary phases formed more bridges to improve the high HTS of 5TiB2/Al-5Cu composites.

A review of microstructural changes occurring during FSW in aluminium alloys and their modelling

Friction stir welding (FSW) process is currently considered as a promising alternative to join aluminium alloys. Indeed, this solid-state welding technique is particularly recommended for the assembly of these materials. Since parts are not heated above their melting temperature, FSW process may prevent solidification defects encountered in joining aluminium alloys and known as limitations to the dissemination of these materials in industries. During the past years, large literature has been devoted to the modelling of microstructural evolution in aluminium alloys during FSW processes and mainly dedicated to the analysis of precipitate evolutions and grain recrystallization mechanisms. Precipitate size distribution models have aroused widespread interest in recent years demonstrating their relevance to follow precipitation process in multicomponent alloys and multiphase systems. Efficient recrystallization models are also available and based on various grain growth mechanisms. In addition, multi-scale coupling strategies have recently emerged considering thermal, mechanical and metallurgical solutions. Consequently, the effect of FSW process parameters on weld properties is now investigated to determine optimized welding strategies regarding microstructure evolution. This research is based on reliable models reported in the literature enhancing the estimation of final weld state and associated properties as an answer to industrial needs. Validations of proposed modelling strategies have been reported based on in-depth analyses of experimental observations. This present work proposes a review of recent models dedicated to microstructural evolutions in aluminium alloys during FSW process. The interest and efficiency of current approaches will be discussed to highlight their limitations. Guidelines will propose new routes toward enhanced modelling strategies for future developments.

Numerical Simulation of Latent Heat of Solidification for Low Pressure Casting of Aluminum Alloy Wheels

In this paper, aiming at focusses on many problems existing in the mathematical model of temperature change in the low-pressure casting solidification process of aluminum alloy wheel hub, there is a big gap between the simulation and the actual temperature change, which affects the research on the solidification defects of the wheel hub. In order to study the solidification behavior of aluminum alloy hub in low-pressure casting process, the mathematical model describing the temperature change in the process of casting solidification is established by using different solidification latent heat methods. through finite element simulation and experiment, the temperature change in the process of aluminum alloy (A356) solidification is obtained to compare the difference between the temperature change described by different mathematical models, simulation and experiment. The results show that the temperature numerical model of "the temperature compensation heat capacity method" proposed in this paper is most consistent with the simulation temperature change during the solidification process of the aluminum alloy wheel in the simulation mold, which lays a good theoretical foundation for the study of the low-pressure casting process of the aluminum alloy wheel hub.

Materials and manufacturing renaissance: Additive manufacturing of high-entropy alloys

Abstract

Application of multi-phase-field lattice Boltzmann method to semi-solid deformation

Mechanisms of semi-solid deformation are crucial for reducing solidification defects. In this study, a multi-phase-field lattice Boltzmann (MPF-LB) model, which can simulate growth of multiple dendrites with liquid flow, solid motion and collision, is applied to semi-solid deformation. An elastic contact is introduced to the MPF-LB model to consider collision of two grains. The semi-solid deformation with globular morphology is simulated in the two-dimension by the MPF-LB method. Through the simulations, high potential of the MPF-LB model as the evaluation method of semi-solid deformation is confirmed.

Solidification, Macrostructure and Shrinkage Formation of Ductile and Compacted Irons

This manuscript summarizes recent investigation of the authors into the solidification and shrinkage defect formation of ductile and compacted graphite cast irons. The study makes use of the DAAS (direct austempering after solidification) technique, developed earlier by some of the authors, to reveal the solidification grains. In addition, color metallography is used to reveal the microsegregation pattern. The formation of shrinkage defects is related to both the solidification macrostructure and the microsegregation pattern. The examination of the macrostructure shows that large solidification grains, composed by dendritic austenite and graphite, characterize the solidification of compacted graphite irons of carbon equivalent values ranging from hypoeutectic to hypereutectic. Similar results are observed for ductile iron, but in this case, the hypereutectic irons display a finer macrostructure. The characteristics of the primary austenite dendrites are revealed by the microsegregation pattern, which is exposed by the color etching reagent. This pattern also clarifies the nature of the interaction between the growing austenite and the compact and spheroidal graphite particles. The microshrinkage cavities in both ductile and compacted graphite irons form at the interior of the austenite grains, where fluid feeding cannot compensate the contraction of the last-to-freeze portions of the melt. Schematics of the solidification of ductile and compacted irons are proposed, accounting for the experimental observations.

Nugget Formation and Characterization of Effect of Cover Plate on the Formation of Solidification Defects in Resistance Spot Welding of Dissimilar Al6016/HC420LA Steel

Herein, 6016 aluminum alloy is joined to HC420LA high‐strength steel by resistance spot welding technology with two kinds of cover plates. The morphology and microstructure of the joint are observed by optical microscopy and scanning electron microscopy. The formation mechanism and control methods of solidification defects such as shrinkage cavities and cracks are discussed. The results show that independent nuggets form on aluminum alloy and high‐strength steel side, respectively, when two kinds of cover plates are added. In some special conditions, the aluminum/steel interface presents a double‐peak shape because of the imbalance between the stress from molten aluminum and that from applied force. Meanwhile, a large shrinkage cavity and longitudinal crack originate from the shrinkage cavity form in the nugget on the aluminum side. All these defects generate in the process of solidification, and a model is established to explain the formation mechanism of solidification defects. Moreover, the control methods to prevent the solidification defects are discussed. Based on the model and control methods, a good joint without solidification defects is produced.

Effect of Electromagnetic Stirring on the Solidification Behavior of High-Magnetic-Induction Grain-Oriented Silicon Steel Continuous Casting Slab

The solidification behaviors of high-magnetic-induction grain-oriented silicon steel slabs have been investigated during experiments in industrial strand electromagnetic stirring (S-EMS). The current intensities of S-EMS were 0, 120, 200, and 350 A, and the frequency was 5 Hz. The ratio of the equiaxed crystal was 14.95%, 15.64%, 45.22%, and 66.96%, respectively. Central porosity cannot be eliminated by increasing the current intensity. The number, size, and ratio of segregation spots were markedly reduced by minimizing the equiaxed crystal zone. Carbon in the 0 and 120 A slabs exhibited a lower degree of macrosegregation compared with the 200 and 350 A slabs. Controlling the cooling rate and increasing the total reduction are the directions to further improve solidification structures, defects, and carbon segregation.

IoT feasibility aspects of mold temperature monitoring and casting simulation for smart foundry

The world is moving in the direction of digitalization demanding change to smart manufacturing. Utilization of smart manufacturing with adoption of Internet of Things (IoT) in the foundry industry gives benefits and help to overcome challenges. In cast iron foundry rejection due to solidification defect like sand drop, crack, pinholes, shrinkage cavity, cold shut, misrun which can be reduced with help of directional solidification. For solidification analysis cooling curve monitoring needs time and effort. For analysis the correct method of data collection and monitor is required. In present work authors have made an attempt to use solution that is anticipated is Autocast_X1 software simulation and development of low cost IoT solution for smart foundry. In Autocast-X1 software simulation is performed and defect analysis is carried out. It is the effective way to improve design and helps to reduce trial runs and efforts. Thermocouple directly placed in a mould cavity to monitor temperature. It is helpful to study cooling curves and quality check of solidification defects. Experimental investigations are carried out to map simulation result of mold temperature with real time data with help of thermocouples placed at mold interface. Mold-metal interface data using controllers and amplifier are stored in mobile for live monitoring. Use low cost IoT platform reduces supervisor movement and saves time by providing casting solidification data at his work place. With the help of casting simulation early check of effective gating system and defect prediction enables reasonable productivity and quality. IoT solution helps to monitor foundry practices, reduction in human effort, paperwork, and reduction in cost with rise of profit margin.

Effectiveness of Feeding System for Enhanced Product Quality in Sand Casting Industries

This review article deals with the importance of process parameters and the recent developments in modern tool technology in the success of smart productivity for casting process of all types. Various influencing factors such as design, location and the number of gating on feeding mechanism were discussed vis-a-vis casting defects. The review revealed reduction in the defects such as air bubbles, blow holes, shrinkage defects and mechanical properties of the casting parts through selection of an optimum feeding design. Variations in fillet radius and thickness on the feeding system were found to be the factors affecting the location of the hot spot. Accordingly, the mobility of the hot spot was controlled by geometrical modifications in the feeding system. In addition, the formation of pinholes and solidification defects could be reduced through a proper arrangement of the feeding system. The rapid growth in implementing simulation techniques in the casting process can assist the enhancement of yield with minimum production cost. This article provides a data base relating to the merits and demerits of various factors and material systems with their industrial applications for enabling further research in the casting process

Microstructure and fatigue behavior of laser-powder bed fusion austenitic stainless steel

The microstructures and stress-controlled fatigue behavior of austenitic stainless steel (AISI 316 L stainless steel) fabricated via laser-powder bed fusion (L-PBF) technique were investigated. For L-PBF process, zigzag laser scanning strategy (scan rotation between successive layer was 0°, ZZ sample) and cross-hatching layer scanning strategy (scan rotation between successive layer was 67°, CH sample) were employed. By inducing different thermal history, it is found that the scan strategies of laser beam have a significant impact on grain size and morphology. Fatigue cracks generally initiated from persistent slip bands (PSBs) or grain boundaries (GBs). It is observed that PSBs could transfer the melt pool boundaries (MPBs) continuously. The MPBs have better strain compatibility compared with grain boundaries (GBs), thus MPBs would not be the initiation site of fatigue cracks. A higher fatigue limit strength could be achieved by employing a crosshatching scanning strategy. For the CH sample, fatigue cracks also initiated from GBs and PSBs. However, fatigue crack initiated from process-induced defects were observed in ZZ sample in high-cycle regions. Solidification microstructures and defects characteristics are important factors affecting the fatigue performance of L-PBF 316 L stainless. Process-induced defects originated from fluid instability can be effectively reduced by adjusting the laser scan strategy.

Quality and yield improvement of ductile iron casting by simulation technique

Foundries contribute to production of major automotive parts. These foundries now a days suffering from poor quality and productivity due to different parameters of the casting process. Casting quality depends on the solidification process after pouring. Computerized casting modeling and solidification simulation is being extensively used by foundries to design the casting process for manufacturing of castings before castings are prepared or before equipment is constructed or improved. The basic objective of using computerized casting modeling and solidification simulation is to increase the quality of the casting manufactured, both in the existing produced casting and first ever castings made and to reduce cost expenses. The shop floor trials can be reduced effectively by casting solidification simulation and defect free castings can be assured. The casting simulation approaches are based on finite element method (FEM), finite difference method (FDM), finite volume method (FVM). In this paper an attempt has been made to use finite difference method (FDM) and finite volume method (FVM) for casting solidification simulation and optimization of casting gating system to assure maximal yield. Modeling and simulation of Flange is analyzed in this study. The material for the flange is ductile iron and produced using shell molding process. Ductile iron has wide range of mechanical properties suitable for production of automotive parts. The 3D model of flange and gating system is created using CATIA and it is simulated using Solid CAST and Auto CAST-X software’s. The simulation software results will predict the location and level of shrinkage. Optimization of gating system will improve casting yield. This will suggest the modifications needed in gating system.

Effects of solidification defects on nanoscale mechanical properties of rapid directionally solidified Al-Cu Alloy: A large scale molecular dynamics study

Directional solidification of Al-11 at % Cu is investigated by molecular dynamics (MD) simulations utilizing second nearest neighbor modified embedded atom method (2NN-MEAM) interatomic potential. The condition for directional solidification is produced by imposing dissimilar temperatures at the model boundaries along the [1 0 0] solidification direction to create a temperature gradient. During solidification, the solid-liquid front travels through the Al-Cu liquid along the [1 0 0] direction towards the high temperature end. At the initial stages of solidification, several solidification defects such as twins, stacking faults, and grain boundaries form. As directional solidification progresses, grains elongate along the solidification direction, and at the final stages of solidification no new defects or grain boundaries form. The elongated grain boundaries form a few layers with lamellar like structures along [1 0 0]. When the solidified polycrystalline is deformed in the [0 0 1] direction, glide of partial dislocations happen around the grain boundaries, whereas during elongation along [1 0 0] some defects from in the Al-Cu matrix. Since formation of defects requires more energy, the solidified samples show a higher tensile strength and strain when deformed along the [1 0 0] solidification direction.

Effect of Solidification Defects and HAZ Softening on the Anisotropic Mechanical Properties of a Wire Arc Additive-Manufactured Low-Carbon Low-Alloy Steel Part

Wire arc additive manufacturing (WAAM) is a pioneer additive-based technology for fabrication of large-scale engineering components. Despite the many advances in the field of additive manufacturing, formation of solidification defects, including discontinuities and microstructural imperfections, in the fabricated components is still inevitable, regardless of the feedstock material or fabrication process applied. In this study, the effects of solidification defects on the anisotropic mechanical properties of a low-carbon low-alloy steel (ER70S-6) wall produced by WAAM have been investigated. Analysis of the microstructure and mechanical properties of the fabricated part confirmed the formation of various solidification defects, i.e., interpass lack of fusions, localized brittle zones, and grain coarsening in the heat-affected zones, leading to anisotropic behavior in the ductility along the deposition versus building directions of the component. The effect of discontinuities on the anisotropic mechanical properties was minimized through microstructural modifications of the fabricated part using postprinting normalizing heat treatment.

Evaluation of the Microstructure and Performance of Fe-21Cr-15Ni-6Mn-Nb Nonmagnetic Stainless Steel Welded Joints

In the present study, double-sided gas shield welding (GSW), in a single pass, was applied to Fe-21Cr-15Ni-6Mn-Nb nonmagnetic stainless steel plate. The microstructure and performance of the welded joint were investigated via microstructural and phase analysis, mechanical testing and magnetic analysis. The results showed a satisfactory micrographic appearance with full penetration, and no solidification defects observed in the welded joint, which showed typical epitaxial growth characteristics in the welding solidification. Slight grain growth, with an average size of ~ 18.9 μm, occurred in the heat-affected zone (HAZ). The primary dendrite arms, on both sides of welding joint, grew along the direction of the temperature gradient and met at the centerline of the weld with no parting microstructure in evidence. The secondary dendrite arm spacing was stable in all parts of the weld zone (WZ). The hardness of the weld zone was higher than that of the HAZ and the base metal (BM), with the lowest hardness occurring in the HAZ. The results of tensile testing showed a higher strength of the welded metal (WM) compared to the BM, and a good strength-ductility balance of the welded joint. The impact energy of the HAZ was higher than that of the WZ, corresponding to 60.5 J at room temperature and 52.7 J at − 196 °C. Microvoid coalescence, concurrent with crack propagation along the direction of the long axis of the dendritic sub-grains, was observed during plastic deformation in the WZ. Additionally, the excellent paramagnetic characteristics of the welded specimens were revealed.

Solidification Defects in Additive Manufactured Materials

Solidification Defects in Additive Manufactured Materials

Correction to: Effects of Recycled Powder on Solidification Defects, Microstructure, and Corrosion Properties of DMLS Fabricated AlSi10Mg

The original version of this article was updated to correct an errant space in AlSi10Mg throughout the text.

Effects of Recycled Powder on Solidification Defects, Microstructure, and Corrosion Properties of DMLS Fabricated AlSi10Mg

This study examines the impacts of using recycled powder on solidification defects, microstructures, and the resultant corrosion properties of direct metal laser sintered AlSi10Mg alloy. Microstructural analysis confirmed that using recycled powder in the fabrication of AlSi10Mg leads to (1) an increased volume fraction of internal porosities and solidification micro-cracks, and (2) more coarsening of the interdendritic eutectic-Si network particularly along the melt pool boundaries, which were correlated to the larger size and irregular shape of the recycled powders compared to the virgin powders, leading to the reduced thermal conductivity of the recycled powders. To investigate the impacts of the above-mentioned microstructural changes on the corrosion performance of the alloy, anodic polarization testing and electrochemical impedance spectroscopy in aerated 3.5 wt.% NaCl solution were performed. The results confirmed a slight degradation of the corrosion properties of the recycled-powder fabricated samples, ascribed to further coarsening of Si-network along their melt pool boundaries.