Casting Defects Research Articles

Fatigue fracture experiment of concrete members with cold joints under low stress and low stress amplitude fatigue load

Currently, numerous studies are conducted on the fatigue fracture performance of concrete, considering various factors such as material ratio, material content, and external environment. However, very few studies consider the impact of casting defects on the fatigue fracture performance of concrete. Cold joints, one of the typical casting defects, are weak joints caused by the discontinuous pouring of concrete structures. To investigate the fatigue fracture performance of concrete with cold joint defects, this study conducted fracture experiments using static load and interface nanoindentation experiments on 12 concrete experimental components with cold joints to analyze the fracture performance and cold joint interface characteristics. Subsequently, this study conducted fatigue fracture experiments on 144 experimental components with cold joints to analyze the fracture characteristics and fatigue life under low stress and low stress amplitude fatigue loads. The results indicate that the peak load, initiation fracture toughness, and unstable fracture toughness of concrete members with cold joints decrease with the extension of the pouring interval of cold joints. The thickness of the cold joint interface increases with the extension of the pouring interval, while the strength decreases with the extension of the pouring interval. The fatigue life of experimental components with cold joints reduces with stress and stress amplitude raising. Under the same initial stress and stress amplitude, the fatigue life of concrete members with cold joints decreases as the pouring interval extends, and the bearing performance deteriorates further after the same number of cyclic loading. Fatigue loads with low stress and low stress amplitudes can lead to the fatigue fracture of experimental components with cold joints. The research findings can serve as a foundation for the study of damage and cracking in lining with cold joints under aerodynamic fatigue loads in high-speed railway tunnels.

Classification of 3D Casting Models for Product Lifecycle Management and Corporate Sustainability

The purpose of this study was to combine simulations and experiments in order to present the first stage of construction in product lifecycle management. Based on the simplification of casting models, the relationship between the filling and solidification characteristics, casting methods, and geometrical classifications of aluminum alloy precision casting products was investigated. By rearranging and summarizing the data, the casting models could be digitally managed; moreover, the digitized data could be used as the basis for intelligent processes in further developments. The simulations calculated and analyzed the casting speeds, defect locations, material densities, and critical fraction of a solid A356 aluminum–silicon alloy; the actual casting was carried out and samples were taken for metallographic observation to confirm the simulation results. The part model was simplified with four basic geometric shapes: solid cylinder, tubular, block rectangle, and thin-shell rectangle. The 150 casting models were summarized using 37 combinations, which were further classified into five main categories to match the casting method: solid cylindrical, tubular, and thin-shell rectangular for side casting, and discoidal and plate rectangular for bottom casting. File-compression rates of up to 75% were achieved after classification and archiving, and data integrity was maintained. Finally, model training using random forest classification resulted in an 88.8% accuracy when predicting the casting method. This research is based on the practical issues raised by business owners and R&D engineers, and a solution was obtained. From the perspective of product lifecycle management, the results of this study show the consistency and uniformity of product design rules, as well as the reusability of product process planning, which can be integrated with carbon emissions trading and carbon taxes to save energy and achieve corporate sustainability.

Damage detection method of automobile hub based on image texture feature

With the rapid growth in the number of motor vehicles worldwide, the general public is beginning to attach importance to the quality inspection of wheels before they leave the factory. The current wheel defect detection systems are often cumbersome to operate and have low practical performance. Therefore, this research will use dynamic image segmentation, image texture feature extraction and Back Propagation neural network classification based on wheel image defect feature analysis algorithm to achieve automatic intelligent detection of automotive wheel defects. In this study, an intelligent detection system for automotive wheel defects is also designed, and finally the performance of the detection system is tested experimentally to illustrate its practicality. The experimental results show that the proposed intelligent detection system for automotive wheel defects based on image texture features identifies defects in wheel castings with a correct rate of 96% and a false positive rate of only 2%. This illustrates that the detection system proposed in this study has a high recognition rate and can provide a useful reference for the automotive industry inspection.

Effect of the Cooling Capability Difference Between Additively Manufactured Sand Molds on Shrinkage Defect in A356 Alloy Castings

Effect of the Cooling Capability Difference Between Additively Manufactured Sand Molds on Shrinkage Defect in A356 Alloy Castings

Numerical simulation of directional solidification process of single crystal blade based on precast

A finite element method was applied to establish a mathematical model of a single crystal blade’s directional solidification process. The model had different angles between the axis of the mold group and the blade. The effects of different radiation angles on temperature variation laws at different blade positions were investigated. The temperature near the center was lower than that near the wall on the upper side of the baffle, while it was higher on the lower side. Moreover, the grain growth of stray particles in blade casting defects was influenced by blade orientation. The grain growth of scattering particles in blade casting defects was faster. The isolated solid-liquid mixing zone was more prone to form at the platform tip near the center when the blade orientation angle was smaller. The 0° orientation angle resulted in the blade’s most severe stray grain phenomenon.

Fracture-based modeling of heat-treated AZ91/AZE911 magnesium alloys for estimating high-cycle fatigue lifetime by Paris crack growth rate and striations spacing

In the present research, the fracture behavior of the AZ91 magnesium alloy is analyzed based on the striations spacing on the fracture surface for predicting the fatigue High-Cycle Fatigue lifetime. At first, equations and relations were extracted based on the Paris law. Then, striations spacing was measured using ImageJ software and field emission scanning electron microscope images of fracture surfaces of heat-treated Mg–Al–Zn alloys, containing and non-containing 1% rare earth elements (1% RE). Finally, constants of the Paris law were calculated and calibrated. Results showed that a 1% RE addition decreased the striations spacing and enhanced the fatigue resistance (between 14 and 40%). In addition, the lifetime scatter band and mean error decreased from ± 2.7X to ± 1.5X and from 150 to 33%, respectively, as the accuracy of the recommended model. Heat-treating transformed the continuous precipitations to blade-shaped precipitations on the Mg-matrix and decreased the grain size remarkably. The addition of 1% RE formed the new Al11RE3 phase and created a better distribution between the cast defects. In addition, fatigue striations in AZ91 alloy had more curvature and discontinuity and were more significant and coarser than those in AZE911 + 1% RE (AZE911) alloy.Graphical abstract

Data-Driven Process Analysis for Iron Foundries with Automatic Sand Molding Process

This paper proposes a methodological framework to develop a data-driven process control using pure industrial production data from a cast iron foundry, despite the limitation of complete casting traceability. The aim is to help sand foundries to produce good castings. A reference foundry, which produces mainly automotive and oven parts with automatic sand molding and pouring machines, was selected. Past data, where only good castings were produced, were extracted from the database to determine parameter control limits (upper and lower control limits) with the aid of statistical approach. To identify critical process parameters associated with casting defects, process data from the zero and high scrap production batches were systematically compared. This method clearly identified unstable parameters without exact synchronization between inline and part quality data. Molding sand moisture, temperature and compactability, liquidus temperature of the melt, phosphorus content, carbon equivalent and pouring temperature were found to be the critical parameters to be stabilized. Finally, a regression model for predicting and controlling of molding sand moisture and liquidus temperature of the melt was created. The determined boundaries and the models were helpful for the foundry in assisting ongoing production control and correction of process inputs to achieve target casting quality.

Preface to the Special Topics on “Quantitative Analysis and Modeling of Solidification Phenomena Related to Macrosegregation and Cast Defect”

Preface to the Special Topics on “Quantitative Analysis and Modeling of Solidification Phenomena Related to Macrosegregation and Cast Defect”

Computer Vision Recognition Method for Surface Defects of Casting Workpieces

<p>To improve the recognition efficiency of surface defects in castings, this article first uses median filtering algorithm to denoise the defect image to distinguish between defects and background. Then, gray threshold method is used to segment the image, and the processed image is sent to the improved RefineDet network structure. Improving the RefineDet network structure mainly improves the network depth and incorporates dataset augmentation algorithms. Finally, an experimental platform was built to train, recognize, and compare the collected image dataset. The results show that the accuracy of detecting porosity, blowhole, and flaw defects is 95.6% and 97.3% and 98.15%, the method proposed in this article is accurate and efficient. </p> <p> </p>

Improvement of Hot Tearing Resistance of AZ91 Alloy with the Addition of Trace Ca.

Hot tearing is the most common and serious casting defect that restricts the light weight and integration of magnesium alloy components. In the present study, trace Ca (0-1.0 wt.%) was added to improve the resistance of AZ91 alloy to hot tearing. The hot tearing susceptivity (HTS) of alloys was experimentally measured by a constraint rod casting method. The results indicate that the HTS presents a ν-shaped tendency with the increase in Ca content, and reaches its minimum value in AZ91-0.1Ca alloy. Ca is well dissolved into α-Mg matrix and Mg17Al12 phase at an addition not exceeding 0.1 wt.%. The solid-solution behavior of Ca increases eutectic content and its corresponding liquid film thickness, improves the strength of dendrites at high temperature, and thereby promotes the hot tearing resistance of the alloy. Al2Ca phases appear and aggregate at dendrite boundaries with further increases in Ca above 0.1 wt.%. The coarsened Al2Ca phase hinders the feeding channel and causes stress concentration during the solidification shrinkage, thereby deteriorating the hot tearing resistance of the alloy. These findings were further verified by fracture morphology observations and microscopic strain analysis near the fracture surface based on kernel average misorientation (KAM).

Analysis of the transformation of the microstructure of axial billets after rolling

The task of improving the quality of metal products of large cross-sections pro-duced from continuous cast billets (CBS) is associated with a number of difficulties. These include the presence of internal defects in the macrostructure of the workpiece (axial looseness, porosity, liquation, crystallization cracks, etc.). Processing from the point of view of deformation of cast workpieces is necessary first of all to eliminate cast defects. An increase in working out contributes not only to the welding of existing mi-crodiscontinuities and, in this connection, to an increase in the density of the metal, but also to the extraction, crushing and reduction of the cross-section of the existing non-metallic inclusions. However, the dimensions of the elements of the primary structure, which are presented on the graphs, are also of the greatest importance. The smallest level of liquation is formed in the surface areas during crystallization. At the same time, as a rule, it is necessary to obtain a homogeneous structure in terms of grain size on the cross-section of large-sized metal products. A study of the features of the structure of axle blanks made of steel grade F (AAR M-101-2017 Axles, carbon steel, heat-treated) after longitudinal rolling on a TPA 5-12" pipe rolling unit with pilgrim mills in three crimping modes (1 mode: Ø 470 → Ø 380 → Ø 260 mm; 2nd mode: Ø 470 → Ø 420 → Ø 260 mm; 3rd mode: Ø 470 →Ø 260 mm). Determination of the features of the distri-bution of deformation work and the formation of the final structure after deformation according to the experimental modes of BLZ Ø470 mm per circle Ø260 mm is the pur-pose of the research. Samples for the structure study were taken both from the original BLZ and the finished draft axle along the entire cross-section. The greatest unevenness of the liquation background, which is observed in the axial blank manufactured using mode No. 1, is also manifested during the study of the microstructure of railway of the axes obtained by the indicated modes. It was determined that the uniformity of the grain structure is the highest after using mode No. 3 (Ø 470 →Ø 260 mm).

Numerical modelling of macrosegregation in three-dimensional continuous casting of steel billets

Macrosegregation presents a considerable defect in the continuous casting of billets and can critically affect the final properties of the product. The numerical modelling can help to predict and better understand the segregation and flow patterns inside the mould. The process is modelled with a physical model described by a set of conservation equations describing the t heat transfer, turbulence, fluid flow, solidification and segregation. A two-equation low-Re k-epsilon model and Abe-Kondoh-Nagano closures are used to close governing equations in this incompressible fluid flow example. The Boussinesq approximation is applied to account for the thermo-solutal buoyancy effects, and the Darcy approximation is applied for the description of the flow through the porous mushy zone. On a microscale, a lever rule solidification model is used to couple liquid fraction, temperature and concentration. The three-dimensional model is solved with the method based on local collocation with multiquadric radial basis functions on seven-nodded subdomains. The aim of this contribution is to explore the three-dimensional macrosegregation patterns of 0.51 wt% carbon steel in the solidified shell of the steel in the mould.

Hot tear prediction in large sized high alloyed turbine steel parts - experimental based calibration of mechanical data and model validation

The main defects in heavy steel castings are related to hot tear formation during solidification. Depending on the steel grade, design, and local solidification conditions, it is possible to predict regions with higher risk of hot tear formation during the casting process. However, steels containing Boron show more complex crack and defect patterns compared to common steel casting alloys. The mechanisms behind the Boron induced hot tearing is investigated in this work to understand the influence of Boron enrichment during solidification and the influence on hot tearing. The experimental work includes the investigation of phase diagrams and the corresponding fractions of the solid and liquid phases depending on temperature using thermal analysis e.g. DSC and HT-LSCM. The hot tearing sensitivity and mechanical properties during solidification are obtained in the Submerged Split Chill Test, SSCT. In addition IMC-B 3-point bending tests are performed to determine high-temperature material properties in the solid state. The work is part of a research project where the final goal is to improve the hot tear predictions based on experimental work and carry out a benchmark simulation of a real sized casting and use it to show the agreement between the numerical results and extensive non-destructive testing from industrial observations.

Determination of the critical drop height and critical flow velocity of aluminum alloy (AL-91% Mg-8% Fe-0.4% Zn-0.2%) in gravity sand casting

Casting is a manufacturing process in which molten metal is poured through the gating system to fill the mould cavity where it solidifies. Variations in casting parameters by different researchers have led to significant variations in casting guidelines, which have forced Foundry Engineers to carry out a number of trial-and-error runs to create guidelines based on their own experience. These variations in guidelines have led to defects occurring in casting during the mould filling process. This work aimed at determining the critical drop height and critical flow velocity of a certain molten aluminum alloy as it flow down the mould sprue in gravity sand casting. The continuity equation was used to describe the velocity distribution of the aluminum alloy as it flows down the sprue. The mathematical tool used in this research is the finite element method. It involves the discretization of the domain of interest into smaller finite elements. The weak form of the governing equation was obtained and integrated over the domain of interest. The results obtained, established the critical flow velocity of aluminum alloy, down the sprue, as 2.565 × 103 mm/s and the critical drop height as 377mm. Results obtained were compared with literature and were also used to produce various casts, it was observed that casts produced, using sprue height below the critical drop height obtained prevented casting defects, while at sprue height above the critical drop height, the danger of casting defects could not be avoided.

Measurement of Exothermic Values of Casting-sleeve Materials Using an Ice Calorimeter

Defects, which are a major problem in casting, can affect the integrity of products. The processes used to reduce defects are often complex and increase manufacturing cost. Simulations are used to predict casting defects by analyzing the flow and solidification of the metal. However, simulation results often differ from actual casting results because appropriate values for the physical properties have not yet been experimentally obtained. Thus, in this study, an ice calorimeter was developed to measure the exothermic value of sleeve materials under rapid heating conditions. In the case where a thermocouple or radiation thermometer is used to determine the heater temperature, heat loss due to the lead wires or hole for temperature measurement cannot be avoided. Therefore, in this study, the heater resistance was obtained using current and voltage, and the temperature was determined using the resistance value. Although some variations were observed, the average measured exothermic values of all exothermic sleeve materials (1.2 kJ/g) matched approximately with those predicted by computer simulation using known thermophysical properties and experimentally obtained distributions of shrinkage cavities. Therefore, the exothermic values obtained in this study are considered valid.

Effects of multi-pass friction stir processing on mechanical and tribological properties of Mg–Zn–Zr alloys

Owing to high strength and good biocompatibility, Mg–Zn binary alloys have attracted significant attention as a potential candidate for producing human implants. However due to the formation casting defects and dendritic structure, these alloys show poor mechanical and wear performances. Alloying and applying severe plastic deformation methods are suggested as two techniques for modifying and improving the above properties. In this study, dry-sliding wear and friction behaviors of the Mg–0.5Zn (MZ) alloy were enhanced by micro-alloying with Zr (0.25 wt%) and applying multi-pass friction stir processing (FSP) technique. Adding Zr reduced the average grain size (AGS) from 1.5 ± 0.3 mm in the MZ sample to about 510 ± 50 μm through the formation of evenly distributed Zr-rich particles with the chemical composition of Mg: 8.84, Zn: 0.75, and Zr: 90.41 A% in the structure. Furthermore, the attendance of thermostable Zr particles stimulated the dynamic recrystallization (DRX) during FSP and reduced the AGS to less than ≈2 μm after the 3rd FSP pass. This substantial grain refinement along with the casting defects reduction, and the fragmentation and redistribution of Zr particles enhanced the hardness and tensile properties of the substrate. Thus, the improved substrate in the FSPed samples, increased the stability of the formed tribolayer on the worn surfaces and changed the wear mechanisms from severe adhesive/delamination in the MZ alloy to mild abrasive/adhesive in the FSPed Zr-modified samples. Therefore, in the optimal condition (3-pass FSPed Mg–0.5Zn–0.25Zr sample), the hardness and total elongation percentage (EL%) increased by 55% and 648% while the mass loss and average friction coefficient (AFC) were reduced by 54% and 39%, respectively, compared to the as-cast Mg–0.5Zn alloy (under a load of 30 N).

Assessing Cast Aluminum Alloys with Computed Tomography Defect Metrics: A Gurson Porous Plasticity Approach

Aluminum alloys have inherent tendencies to produce casting defects caused by alloying or metal melt flow inside the mold. The traditional detection method for these defects includes reduced pressure tests, which assess metal quality in a destructive manner. This leaves a gap between metal quality assessments and tensile test correlations. Computed tomography (CT) scans offer crucial assistance in evaluating the internal quality of castings without damaging the structure. This provides a valuable opportunity to couple mechanical tests with numerical methods such as finite element analysis to predict the mechanical performance of the alloy. The present study aims to evaluate the internal quality of cast aluminum alloys using CT scans and to correlate the defect metrics obtained from CT scans with mechanical test results. The Gurson-type material model and finite element methodology have been used to validate the correlation studies. Therefore, we propose a more holistic approach to predicting the behavior of metals by coupling damage models with CT scans and mechanical tests. The study investigates several CT metrics such as the defect volume, total defect surface, biggest defect surface, and projected area of defects. The conclusion reveals that CT scans provide crucial assistance in evaluating the internal quality of castings, and CT defect metrics can be used to build correlations between mechanical tests and CT evaluations. The study also suggests that the concept of adjusted representative material yield parameter (ARMY) or computed representative material yield parameter (CRMY) can be used to correlate CT metrics with mechanical strength in cast materials and parts for a given aluminum alloy. Overall, the study proposes a more comprehensive methodology to assess the quality of cast aluminum alloys and couple the quality to mechanical performance.

Impact of Titanium Addition on Microstructure, Corrosion Resistance, and Hardness of As-Cast Al+6%Li Alloy

Aluminum-lithium alloys have the potential for use in aerospace applications, and improving their physical, mechanical, and operational characteristics through alloying is a pressing task. Lithium, with a density of 0.54 g/cm3, enhances the elastic modulus of aluminum while reducing the weight of the resulting alloys, making them increasingly attractive. Adding transition metal additives to aluminum alloys enhances their strength, heat resistance, and corrosion resistance, due to their modifying effect and grain refinement. The study aimed to investigate the impact of titanium content on the microstructure, corrosion resistance, and hardness of Al-Li alloys. Four alloys were prepared with varying amounts of titanium at 0.05 wt%, 0.1 wt%, 0.5 wt%, and 1.0 wt%. The results showed that the microstructure of the alloy was modified after adding Ti, resulting in a decrease in average grain size to about 60% with the best refinement at 0.05 wt% Ti content. SEM and EDS analysis revealed an irregular net-shaped interdendritic microstructure with an observed microsegregation of Al3Li compounds and other trace elements at the grain boundaries. The samples showed casting defects due to the high content of Li in the alloy, which absorbed air during casting, resulting in casting defects such as shrinkage holes. The corrosion resistance test results were low for the samples with casting defects, with the least resistance recorded for a sample containing 0.1 wt% Ti content, with more casting defects. The addition of Ti increased the microhardness of the alloy to an average of 91.8 ± 2.8 HV.

Effects of die-casting defects on the blister formation in high-pressure die-casting aluminum structural components

The following work aims to present the casting defects effect in AlSi10MnMg alloy structural components on the blister’s possibility. Structural components must exhibit high mechanical properties, specifically high ductility. That requires the heat treatment process. However, the component’s exposure to high temperatures can cause blistering on the surface, which is unacceptable in the final product.For microstructure studies, the samples were cut from regions close to the gating system (hot areas) and those away from it (cold areas). For comparison, the paper studied castings in the as-cast state and after T7 heat treatment. The results suggest that the blistering process begins at casting defects, which create microstructural discontinuities. If gases are present in a discontinuity, they expand during solution treatment, forming surface blisters. The largest blisters form on cold flakes, mainly in casting areas near the gating system.However, smaller blisters form on porosity - both gas and shrinkage. The last casting defects that act as blistering sites are cold drops, cold shots, and thin oxide films occurring mainly in areas away from the gating system.

Gift for the gods or scrapping over scrap metal? Metallographic examination of sword fragments from the Late Bronze Age hoard from Slavonski Brod, Croatia

Abstract The deposition of metal in hoards appear throughout the European Bronze Age and there is on-going dispute about motivations behind the practice of hoarding metals at that period. Therefore, nine fragments of bronze swords from a late Bronze Age hoard have been investigated by metallography and X-ray fluorescence analysis (EDXRF) in order to evaluate their conditions. The objects do not show compositional deviations from contemporaneous material, but they are of poor quality showing considerable casting defects and pronounced dendritic segregation. They may never have been finished. Nonetheless, the reasons for their destruction and burial do not become evident.