Investigation on interface of Al/Cu couples in compound casting

Abstract

The joining of Al and Cu commercially pure metals using the compound casting process has been investigated where an aluminium melt is cast onto a solid cylindrical copper insert. The microstructure of the interface between copper core and surrounding aluminium was characterised by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and Vickers hardness tests. Results showed that five separate reaction layers are formed in the reaction interface of core and surrounding Al. These layers included Cu₉Al₄, AlCu and Al₂Cu intermetallic compounds; a eutectic layer; and a eutectic α-Al dendritic structure layer. Owing to the presence of hard and brittle intermetallic compounds within reaction layers, microhardness profile showed a peak of 300 HV where both parent metals have hardness <50 HV. Microhardness profile also showed that hardness decreases from the copper to the aluminium side.     

铸造铝合金半连续铸棒组织与性能均匀性研究

目的 研究ZL114A合金和ZL205A合金半连续铸棒不同部位的力学性能与微观组织,分析铝合金半连续铸棒的均匀性。方法 分别对半连续铸棒的中心位置、R/2位置、边缘R位置进行取样,对比分析各部位的力学性能及微观组织。结果 ZL114A合金的抗拉强度为338~355 MPa,断后伸长率为9%~11.5%;ZL205A合金的抗拉强度为465~485 MPa,断后伸长率为12%~15%。与铸棒中心位置相比,铸棒边缘R位置的晶粒尺寸更小,性能也更优异,但ZL114A合金铸棒的边缘R位置存在夹渣缺陷,导致其力学性能低于铸棒中心位置的力学性能。结论 采用半连续铸造工艺制备的ZL114A合金和ZL205A合金均具有细小、均匀的微观组织,且组织越细小的部位,力学性能越高,存在凝固缺陷的部位,力学性能较低。     

Roman situlae from Conimbriga (Portugal): Compositional and microstructural characterization of anthropomorphic handle attachments

ABSTRACT

A collection of 33 anthropomorphic handle attachments of Roman situlae recovered from the archeological site of Conimbriga (Central Portugal, 2nd century BC–5th century AD) was studied by micro-Energy Dispersive X-Ray Fluorescence Spectrometry (micro-EDXRF), Scanning Electron Microscopy - Energy Dispersive Spectroscopy (SEM-EDS) and metallographic techniques. Regarding the characterization of Roman artifacts of regional production, the relation among typology, composition and microstructure was evaluated in order to infer the Roman influence on the copper metallurgy in Western Iberia. The collection was found to be heterogeneous, mainly constituted by leaded copper and leaded bronzes, with a wide range of lead contents. The artifacts were all produced by mold casting, and most of them show some post-casting processing. Important casting faults and broken artifacts were associated with higher lead contents, and were mainly leaded copper. The leaded bronzes were more carefully produced. The overall results suggest a local metallurgical tradition, with the usage of copper and copper alloy scraps, with high additions of lead. The aim was to produce colored (and cheaper) artifacts, without any major concerns about the finishing details.     

Improvement of mechanical properties of cast pure titanium by repeated heat treatment

ABSTRACT

Pure titanium components fabricated by casting have a coarse grain microstructure. To improve the mechanical strength of pure titanium components by refining the grain size, the cast samples were repeatedly heat-treated. During the heat treatment, the titanium samples were repeatedly heated above the alpha-to-beta (α–β) transition temperature and cooled to room temperature to undergo phase transformation. The heating cycle was performed 1, 3, 5, and 7 times. As the number of heating cycles increased, the grain size decreased. The tensile strength was 267.9?MPa in the as-cast sample and improved to 343.4?MPa after 7 heat-treatment cycles owing to the grain size refinement, while the elongation was maintained during the heat treatment.

This paper is part of a thematic issue on Titanium.     

Numerical simulation of the temperature field in the electromagnetic semi-continuous casting of slab

Electromagnetic casting of aluminum is a semi-continuous casting process and the corresponding mathematical model is a non-steady non-homogeneous heat-transfer equation. This paper indicates and testifies that the dynamic temperature field can be calculated with a three-dimensional non-steady homogeneous heat-transfer equation. The software program has universal use. Further, a casting process of 1860 × 510 mm aluminum slab is simulated, the results agreeing well with those reported in the literature.     

Ultrasound effect on structure and properties of Cu–0.5Cr under upsetting

ABSTRACT

We studied the effect of the regimes of ultrasonic action on the structural transformation during free upsetting with 50% reduction of the copper alloy Cu–0.5Cr. In the process of deformation, the samples were subjected to intermittent and continuous ultrasonic actions. It can be noted that the application of ultrasonic vibrations in the process of deformation leads in both cases to a reduction in yield strength. Under a continuous ultrasonic action with a power of 640?W, the most developed structure is formed, with a fraction of high-angle boundaries equal to 32.4%, with the lowest values of coherent scattering regions, density of dislocations and microdistortions, while the decline in yield strength of the material under deformation is 40?MPa.

This paper is part of a Thematic Issue on Copper and its Alloys.     

4045/3004/4045层状铝合金复合材料连铸制备方法

本文旨在开发出制备复合锭坯的新技术,在新型热顶石墨环结晶器中安装冷却板,采用直接水冷半连续铸造法实现了4045/3004/4045铝合金三层复合锭的实验室制备,研究了复合锭坯的宏观形貌、微观组织,并考察了界面两侧元素分布以及铸造过程中界面附近3004合金熔体的温度分布.结果表明:在冷却板的作用下界面附近形成了一层温度分布较为均匀的固态支撑层,从而保证复合铸造过程的顺利实现,复合界面结合较好,且为一种冶金结合;由界面抗拉强度测试结果可知界面的结合强度均高于96 MPa,进一步证明了两种合金的结合是一种冶金结合.     

Semisolid processing of short and long freezing range Cu alloys by electric current

Abstract

The present study reports the effect of ac (50 Hz) electric current treatment (ECT) on short freezing range (Cu–Ni) and long freezing range (Cu–Sn) alloys. This treatment was conducted during the semisolid state of the alloys, i.e. during casting in sand moulds. In isomorphous Cu–Ni alloy, with gradual increase in the electric current, first, the dendrites are refined; then, the refined dendrites are fragmented; and finally, the fragmented dendrites are refined. The ECT also reduces homogenisation treatment time. It is observed that a small amount of electric energy spent during sand casting saves considerable amount of energy for homogenisation treatment. The sand castings of Cu–Sn (peritectic) alloys are very much prone to interdendritic shrinkage. Thus, the density of castings is reduced. However, the ECT during casting increases the density of castings by reducing interdendritic shrinkage, modifies phase diagram of Cu–Sn alloy, increases volume fraction of the primary α phase (Cu) and reduces volume fraction of the peritectic phase. The ECT also refines the peritectic phase that transforms to δ phase on cooling to room temperature.     

Modelling and simulation of the electric slag remelting guide vane casting (ESRC) process and its application

Modelling and experiment work is carried out for a large stainless steel casting with variable cross-section and a curved surface which is produced by the electric slag remelting casting process. The casting is part of a hydraulic runner generator at a power station of a big river.

Mathematical models of the heat transfer and melted rate from an expendable metallic electrode were established. The melted rate is related to some important parameters, such as electric current and voltage, temperature and the flow rate of the cooling water in a crystallizer. Electrode melting, the moving pattern of the melted pool and the slag pool and the melt solidification in the metal pool were simulated.

In order to make the enmeshment of the variable curved surface of the casting, a co-operation method of extended constructive solid geometry (CSG) from 9 to 21 uniform geometry with B-Spline surface functions is developed. By this method the guide vane casting is enmeshed. The boundary condition between the steel casting and the crystallizer cooled by water was measured.

Based on the above new content the solidification simulation software ESRC3D is developed. Using it to simulate the whole process of ESRC with different parameters, instead of exploring the technological parameters of casting production by the trail-and-error method, the optimized parameters from the simulation for production of the large stainless steel castings with variable cross-section and a curved surface, such as the guide vane castings, have been used to produce them. Economic benefit and good quality of castings are obtained. Guide vane castings are widely applied to the hydraulic runner generator at numerous river power stations.     

Grain refinement of DC cast AZ91D Mg alloy by intensive melt shearing

Abstract

Melt conditioning by advanced shear technology (MCAST) is a new process for microstructural refinement of both cast and wrought magnesium alloys. Melt conditioned direct chill (MCDC) casting combines the MCAST process with conventional direct chill (DC) casting. In the present work, melt conditioning has been combined with permanent mould casting to simulate the production of DC cast AZ91D billets and slabs. The results show that the MCDC process can achieve significantly finer grain size and more uniform microstructure than conventional DC process for both billets and slabs. Grain refinement in the MCDC process is due to the fine and well dispersed oxide particles produced after processing in the MCAST unit.     

Microstructural,mechanical and electrochemical characterisation of biomaterial ASTM F745 cast by vacuum

Abstract

Countergravity low pressure casting (CLA) was performed to enhance the properties of ASTM F745 stainless steel (SS), which is usually used as biomaterial. The macro- and microstructures were compared with those obtained by the conventional process of investment casting (IC). The SS cast by CLA (SSCLA) exhibited a smaller size of solidification cell and finer dendritic microstructure. The average of its dendritic primary spacing was 110·4 μm, while for the same steel cast by IC (SSIC), it was 186·7 μm. The density of non-metallic inclusions δ_I in the SSCLA was 717 I mm^?2, being the majority of them smaller than 1·5 μm. In the case of SSIC, δ_I was 852 I mm^?2, with a size distribution of up to 8 μm. The SSCLA showed a higher breakdown potential than the SSIC, the values being 0·300 and 0·210 V(saturated calomel electrode) respectively, which means a higher resistance to suffer localised corrosion. Finely, the CLA process also allowed obtaining better mechanical properties.     

Kinetics of transient liquid phase diffusion bonding process for joining aluminium metal matrix composite

Abstract

The mechanism and kinetics of the transient liquid phase diffusion bonding process in a 6061–15 wt-%SiCp composite at 570°C, 0·2 MPa, with 200 μm thick copper foil interlayer, has been investigated by microstructural characterisation of the bond region using optical microscopy, scanning electron microscopy and electron probe microanalysis. The kinetics of isothermal solidification, representing the displacement of the solid/liquid interface y (in micrometres) as a function of time t (in seconds), followed a power law relationship y?=?157t^0·07. According to this kinetic equation, the effective diffusivity of copper in the composite system was found to be ～10⁶ times higher than the lattice diffusivity, indicating the dominance of short circuit diffusion through the defect rich particle/matrix interface.     

Early technologies for metal production in the Iberian Peninsula

ABSTRACT

This paper focuses on the characterization of technological processes used for producing copper, tin-bronze and silver in the Prehistory and Protohistory of the Iberian Peninsula. To this purpose, slags and slaggy materials have been analyzed by optical microscopy (OM) and scanning electron microscopy (SEM-EDS). In particular, the results obtained allow us to characterize the main technological features for smelting copper ores since the 3rd millennium BCE, a process that was performed in simple fire structures using a non-slagging process. Regarding tin-bronze, the analytical data suggest that prehistoric bronzes were obtained by co-smelting copper and tin oxidic ores or by cementation of copper with cassiterite. Finally, some metallurgical debris dated to the Phoenician time, in the early 1st millennium BCE, points to the extraction of silver from argentiferous copper ores employing a method similar to the 15th century liquation process. This is a unique discovery to date as this type of materials is unknown in any other Mediterranean region settled by the Phoenicians.     

铸渗法制备铜基表面复合材料

利用铸渗法对铜合金表面进行改性, 用Fe 基合金粉末作为渗剂在负压条件下进行浇注制备铜基表面复合材料。实验结果表明: 在本实验工艺条件下, 在铜合金铸件的特定表面获得了致密的组织结构不同于基体的渗层———表面复合材料层。经SEM 观察, 发现渗剂颗粒与基体的界面结合良好, 证实了铸渗法制备铜基表面复合材料的可行性。     

Modeling and experimental study for horizontal twin‐roll casting of copper/aluminum clad sheet

A mathematical model has been developed and validated for the horizontal twin‐roll casting of copper/aluminum clad sheet. The influences of the heat transfer coefficient for copper/roll interface, casting speed and clad sheet thickness on the sump depth and temperature distribution of the copper/aluminum interface were studied. The interface morphologies and chemical compositions of the intermetallic compound layers were analyzed. The results showed the sump depth decreased with the increase of heat transfer coefficient for copper/roll interface and moved to the outlet with the increase of the casting speed. Casting speed was linear with the sump depth ratio to set‐back distance on the centerline for different clad sheet thicknesses. The thickness of the intermetallic compound layer increased with the increase of the clad sheet thickness. Only Al₂Cu layer formed on the copper/aluminum interface with clad sheet thickness of 6 mm, and the second layer of Al₄Cu₉ formed near the copper side with the increase of the thickness.     

Interfacial precipitation in hot isostatically pressed diffusion bonds of 17-4 PH stainless steel

Abstract

The embrittlement of hot isostatically pressed (hipped) diffusion bonds manufactured from 17-4 PH stainless steel has been investigated by Auger electron spectroscopy (AES) of in situ fracture specimens. Depth profiling by AES has revealed copper precipitation at the interface of the diffusion bond. This precipitation, up to a few monolayers in thickness, occurs during the ramp up to temperature and pressure of the hot isostatic pressing (hipping) cycle and is not readily removed by subsequent heat treatment. This effect is explained in terms of the metallurgical characteristics of copper within the steel. Results suggest that the extent of the precipitation decreases with increasing process temperature. In the case of PH 13-8 Mo stainless steel, where the precipitation hardening phase is NiAl, the interface is weakened by sulphur segregation and the formation of oxide particles.     

Experiments on interaction of liquid tin with solid copper

Abstract

The reaction of liquid tin with solid copper has been studied by heating small volumes ofpure tin on copper coupons at various temperatures and times, and evaluating the resulting reaction metallographically. Three reaction temperatures were used:260,400,and450 ° C. Specimen geometry was chosento simulate a typical solder joint. The reaction was observed to occur in two stages: an initial fast stage with copper/liquid tin interface movement rates from 0.2 μm s^-1 at260 ° C to 0.8 μm s^-1 at 450 ° C, followed by a much slower stage. It was concluded that the first stage corresponds to direct dissolution of copper in liquid tin up to or beyond the liquidus concentration for the reaction temperature used.This is followed by the formation of an intermetallic compound layer atthe copper/liquid interface. Subsequent copper dissolution then occurs by solid state diffusion through the compound layer, a much slower process than direct dissolution.     

Diffusion samples as a high-throughput screening method for alloy development

ABSTRACT

Diffusion couples of copper alloys are presented as screening tool for high-throughput alloy development. It allows estimating the precipitation hardening potential in multicomponent alloys of a vast number of compositions within one sample. The components were diffusion welded and annealed to form compositional gradients which were characterised through a grid of energy dispersive X-ray spectroscopy measurements. After splitting the different sample parts underwent different tempering treatments. Thereafter micro hardness grids matching the spectroscopy data were recorded and displayed in contour plots as a function of alloy composition that instantly show composition areas with hardening potential. A critical assessment of the reliability of the method is provided and checked for cu-Al/mn-Sn-ti systems against literature data.

This paper is part of a Thematic Issue on Copper and its Alloys.     

Development of an interactive simulation system for the determination of the pressure-time relationship during the filling in a low pressure casting process

An interactive computer simulation system has been developed in this study to aid the determination of the pressure–time relationship during the filling of a low pressure casting to eliminate filling-related defects while maintaining its productivity. The pressure required to fill a casting in a low pressure casting process can be separated into two stages. The first stage is to exer pressure to force the molten metal to rise in the riser tube up to the gate of the casting die, whichvaries from casting to casting due to the drop of the level of the molten metal in the furnace, whilst the second stage is to add an additional pressure to push the molten metal into the die cavity in away that will not cause much turbulence and have the proper illing pattern to avoid the entrapment ofgas while maintaining productivity.

One of the major efforts in this study is to modify the filling simulation system with the capability to directly predict the occurrence of gas porosity developed earlier to interactively determine the proper gate velocity for each and every part of the casting. The pressure required to ill the die cavity can then be obtained from the simulations.

The operation principles and the interactive analysis system developed are then tested on an automotive wheel made by the low pressure casting process to demonstrate how the system can aid in determining the proper pressure–time relations, the p–t curve, required to produce a sound casting without sacrificing productivity.     

Continuous semisolid extending extrusion process for producing AA2017 aluminium alloy flat bar

Abstract

A novel testing machine for a continuous semisolid extending extrusion process (CSEP) has been designed and used to produce AA2017 alloy flat bar. Fine and homogeneous grains of AA2017 slurries with rosette structures were obtained at suitable casting temperatures. During preparation of semisolid AA2017 alloy by the proposed process, rosette grain formation was observed during the application of the large force provided by the rough roll. By controlling casting temperature, AA2017 products were produced with fine surfaces and rectangular transections of 14 × 25 mm. A casting temperature range of 710–750°C was suggested. The microstructure of the product is fine and even with striped appearance and is composed mainly of θ and α phases. The fracture strength of AA2017 product produced by the semisolid extending extrusion process is improved by 100 MPa, and elongation by 29%.