Ke Qin

A microstructural and crystallographic investigation of the precipitation behaviour of a primary Al3Zr phase under a high magnetic field

The effects of a high magnetic field on the precipitation behaviour of the primary Al3Zr phase are investigated. With and without the field, the primary Al3Zr crystals possess three morphologies – small tabular crystals in the deposit layer, long bars and dendritic crystals. The dendritic crystals are probably those surviving from the initial material. The tabular crystals in the deposit layer are those surviving from the heating stage, whereas the long bars are those formed during cooling. With the field, the tabular crystals in the deposit layer and the long bars tend to orient with the 〈110〉 direction parallel to the field direction, but the orientation of the dendritic crystals is less affected. The orientation of the crystals in the deposit layer arises from their magnetocrystalline anisotropy, but that of the long bars and dendritic crystals is disturbed by gravity and the formation of compound twins, respectively. Increased Zr content raises the precipitation amount of the primary Al3Zr crystals but weakens the alignment tendency of the tabular ones in the deposit layer. The weakness of the alignment arises from interaction between the crystals.

Microstructure and properties at bonding interface of AA4045/AA3003 aluminum alloy cladding billet prepared by semi-continuous casting

Abstract AA4045/AA3003 cladding billet was prepared by direct chill semi-continuous casting process. The macrostructures, microstructures, temperature distribution, compositions distribution and the mechanical properties at the bonding interface were investigated in detail. The results show that the cladding billet with few defects could be obtained by semi-continuous casting process. At the interface, diffusion layer of about 10 μm on average formed between the two alloys due to the diffusion of alloy elements in the temperature range from 596 to 632 °C. From the side of AA4045 to the side of AA3003, the Si content has a trend to decrease, while the Mn content has a trend to increase gradually. Tensile strength of the cladding billet reaches 103.7 MPa, the fractured position is located on the AA3003 side, and the shearing strength is 91.1 MPa, revealing that the two alloys were combined metallurgically by mutual diffusion of alloy elements.

The evolution of microstructure and mechanical properties during high-speed direct-chill casting in different Al–Mg2Si in situ composites

The effect of high-speed direct-chill (DC) casting on the microstructure and mechanical properties of Al–Mg2Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al–Mg2Si composites and AA6061 alloy was examined by optical microscopy, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The results revealed that an increase of the casting speed substantially refined the primary Mg2Si particles (from 28 to 12 μm), the spacing of eutectic Mg2Si (from 3 to 0.5 μm), and the grains of AA6061 alloy (from 102 to 22 μm). The morphology of the eutectic Mg2Si transformed from lamellar to rod-like and fibrous with increasing casting speed. The tensile tests showed that the yield strength, tensile strength, and elongation improved at higher casting speeds because of refinement of the Mg2Si phase and the grains in the Al–Mg2Si composites and the AA6061 alloy. High-speed DC casting is demonstrated to be an effective method to improve the mechanical properties of Al–Mg2Si composites and AA6061 alloy billets.

Effect of Compound Modification and Cooling Rate on Microstructure and Mechanical Properties of Al-25%Si Alloy

The effect of phosphorus on primary silicon, phosphorus and mischmetal (Ce-50La) modification on primary and eutectic silicon and cooling rate on microstructure of Al-25%Si are investigated. The results show that, with the addition of phosphorus, the size of primary silicon decreases from 93.6μm to 24.75μm. The morphology of primary silicon changes from irregular to polygonal. When Al-25%Si is modified by phosphorus and mischmetal, primary and eutectic silicon all change effectively. Addition of mischmetal on the basis of phosphorus modification have no influence to primary silicon, but it can make morphology of eutectic silicon change from lamellar to short rod-like when the content of mischmetal reaches 0.5%. The cooling rate curves show the change of temperature in different height of wedge-shaped mould. When cooling rate increases, microstructure of Al-25%Si refines, the size of primary silicon decrease to 22.7μm. The results obtained from mechanical testing demonstrate that the addition of mischmetal and increasing of cooling rate increase hardness value of Al-25%Si alloy.

Effect of Direct Chill Casting Speed and Heat Treatment on Microstructure and Mechanical Properties of Al-13.9%Mg2Si Composite

The aim of this work is to investigate the effect of different casting speed in DC casting process and solution heat treatment of in situ Al-13.9%Mg2Si composite. The increasing of DC casting speed not only makes primary Mg2Si distribute more uniform and restricts segregation of primary Mg2Si particles, but also it reduces primary Mg2Si particle size. The DC casting speed significantly alter the eutectic Mg2Si phase from fibrous to fine dot-like and eutectic phase refines effectively. The results obtained from mechanical testing demonstrated that the increasing of DC casting speed intensifies both hardness and tensile strength values. Then, the billet were subjected to solutionizing at 500oC for holding time of 4h followed by quenching. The results indicate that the morphology of both primary and eutectic Mg2Si changes after heat treatment. Solutionizing leads to the dissolution of the Mg2Si particles and changes morphology from sharp edges to round shape. After solution heat treatment, tensile strength and elongation increase to 238.8MPa and 13.5%.

Numerical simulation and experiment validation of level-pour direct-chill casting of A390 alloy hollow billets under different feeding schemes

Purpose – The purpose of this paper is to study the effect of feeding scheme on melt flow and temperature field during the steady-state of level-pour direct-chill (DC) casting of A390 alloy hollow billet and optimize the design of feeding scheme. Design/methodology/approach – Melt flow and temperature field are investigated by numerical simulation, which is based on a three-dimensional mathematical model and well verified by experiments. Findings – The numerical results reveal that both melt flow and temperature field are obviously affected by the feeding scheme. The homogeneity of melt flow and temperature field in hollow billet with the feeding scheme of modified four inlets are better than the other feeding schemes. Experimental results show that crack can be eliminated by increasing the number of feeding inlets. The primary Si size appears unaffected while the distribution of primary Si particles is highly affected by the change of feeding scheme. Only with the feeding scheme of modified four inlets c...

Numerical simulation on sprue distributions during cladding casting process

Purpose The purpose of this paper is to investigate the influence of sprue distributions on the flow field and temperature field of the cladding casting process and verify the simulation results by experiments. Design/methodology/approach A steady-state mathematic model for the coupling of fluid flow, heat transfer and solidification to describe the process of cladding casting was present. The effect of sprue distributions on melt flow and temperature field was discussed. Based on the numerical simulation results, the cladding billet was prepared successfully. Moreover, the model has been verified against by temperature measurements during the cladding casting process. Findings There is a good agreement between the measured and calculated results. The homogeneity of melt flow determines the formability of cladding billets and circular temperature difference affects the bonding of the two alloys. The AA4045/AA3003 cladding billet with no defects in size of f140/f110 mm was fabricated successfully. The alloy elements diffused across the interface and formed diffusion layer with a thickness of 15 µm. The interface bonding strength is higher than the tensile strength of AA3003, indicating the metallurgical bonding between two alloys. Research limitations/implications The casting parameters are limited to the aluminum alloy cladding billet in size of f140/f110 mm in this paper. Originality/value There are few reports of cladding billet, which are used to prepare condense pipes of automotive engines. The effect of distribution schemes on the cladding casting process is rarely studied.

Interfacial characteristics and properties of a low-clad-ratio AA4045/AA3003 cladding billet fabricated by semi-continuous casting

A low-clad-ratio AA4045/AA3003 cladding billet was fabricated using a semi-continuous casting process and was subsequently extruded indirectly into a cladding pipe. The temperature distribution near the interface was measured. The microstructures, elemental distribution, Vickers hardness around the bonding interface, and the interfacial shear strength were examined. The results showed that the interface temperature rebounded when AA4045 melt contacted the supporting layer. The two alloys bonded well, with few defects, via the diffusion of Si and Mn in the temperature range from 569°C to 632°C. The mean shear strength of the bonding interface was 82.3 MPa, which was greater than that of AA3003 (75.8 MPa), indicating that the two alloys bonded with each other metallurgically via elemental interdiffusion. Moreover, no relative slip occurred between the two alloys during the extrusion process.

Study on Composite Interface of 4045/3003 by Cladding Casting

With the cladding casting equipment, which was self-designed and self-made, 4045/3003 composite ingot, which is in size of Φ140mm/Φ110mm, has been manufactured by direct cooling continuous casting by adjusting and optimizing the technological parameters. The process was investigated involving macro-morphology and microstructure near the interface between the two different aluminum alloys at different positions, and distributions of both components and hardness of the cladding ingot. In addition, the tensile strengths were tested. The results showed that metallurgical bonding of two different aluminum alloys could be obtained by direct-chill semi-continuous casting process. The diffusion layer, which is about 15μm on average, has formed on the two sides of composite interface during casting process. From the side of 4045 aluminum alloy to the side of 3003 aluminum alloy, the Si content has a trend to decrease, as well as the hardness, while the Mn content has a trend to increase gradually. Tensile strength of the coated ingot reaches 117.3MPa, which is higher than the core-material matrix (3003 aluminum alloy), indicating the bonding of the two alloys belongs to metallurgical bonding.

The Numerical and Experimental Study on DC Casting Process of Three-Layer Composite Ingots of 4045/3004/4045 Aluminum Alloys

In this study, experiments are combined with numerical simulation to study the temperature field and flow field during the casting process of 4045/3004/4045 three-layer composite ingots with section of 500mm×420mm. The effects of casting temperature, casting speed, contacting height and cooling intensity of cooling plate on the casting process were discussed. The macro-morphologies and microstructures of the composite ingots, the temperature distribution and the element distribution in the interface zone were investigated, also the interface bonding strength was measured. The optimal parameters for casting composite ingots were obtained. Results show that the solid supporting layer formed on the cooling plates plays a key role in the casting process of composite ingots. The solid supporting layer can prevent the blending of two melts by resisting the impact of alloy melt, which ensures the stable casting process and casting high quality composite ingots.