Wei-min Mao

Effect of pouring temperature on semi-solid slurry of A356 Al alloy prepared by weak electromagnetic stirring

Abstract The semi-solid slurry of A356 Al alloy was manufactured by low superheat pouring and weak electromagnetic stirring. The effects of pouring temperature on the slurry manufactured by weak electromagnetic stirring were researched. The results indicate that it is feasible to manufacture the slurry with particle-like primary phases by low superheat pouring and weak electromagnetic stirring, and there is an important effect of the pouring temperature (superheat temperature) on the morphology and the size of primary a -Al in A356 Al alloy. By the action of suitable weak electromagnetic stirring, increasing pouring temperature to put low superheat pouring in practice is capable of obtaining semi-solid slurry of A356 Al alloy with particle-like primary phase. Compared with the samples made only by low superheat pouring without stirring, raising pouring temperature by 15–35 °C above the liquidus temperature under condition of weak electromagnetic stirring can ensure the same grain size and morphology of the primary phase.

Influence of process parameters on microstructure of semisolid A356 alloy slug cast through vertical pipe

Abstract Suitable microstructures required for semisolid casting were formed by using a vertical pipe. Different lengths of vertical pipe, slug dimensions and pouring time were used to investigate their influence on the microstructure of A356 alloy. The results indicate that at the same length of the vertical pipe, the morphology of the primary α (Al) gradually deteriorates by the enlargement in the slug size, but the deteriorating speed slows down with increasing pipe length. They also reveal that the increase in the pipe length improves the microstructure, whereas no further improvement appears when the pipe length reaches a certain value. The optimum length of the pipe obtained in the present work is 430 mm. The microstructure of larger slug poured at higher pouring temperature gets worse and it can be improved by moderately elongating pouring time. The relative mechanisms were also discussed.

Preparation of semi-solid 7075 aluminum alloy slurry by serpentine pouring channel

Abstract The semi-solid slurry of 7075 aluminum alloy was prepared by a serpentine pouring channel (SCP). Influences of pouring temperature and the number of turns on the microstructure of semi-solid 7075 alloy slurry were investigated. The results demonstrated that the semi-solid 7075 aluminum alloy slurry with satisfied quality could be generated by a serpentine pouring channel when the pouring temperature was in the range of 680–700 °C. At a given pouring temperature, the equivalent size of the primary α(Al) grains decreased and the shape factor increased with the increase of the number of turns. During the slurry preparation of semi-solid 7075 aluminum alloy, the flow direction of alloy melt changed many times when it flowed in a curved and closed serpentine channel. With the effect of “stirring” in it, the primary nuclei gradually evolved into spherical and near-spherical grains.

Microstructure evolution of semi-solid 7075 Al alloy slurry during temperature homogenization treatment

Abstract Semi-solid 7075 Al slurry was prepared by inverted cone-shaped pouring channel process (ICSPC) and temperature homogenization (TH) treatment was combined to make the slurry uniform and have a controllable solid fraction suitable for the follow-up rheocasting. The influence of cooling rate on the microstructure evolution of primary α (Al) during TH treatment was investigated. The results show that as the cooling rate of the slurry after being prepared reduces, the growth of primary α (Al) in the slurry tends to be nearly spherical and the uniformity of the organization is also enhanced. This may be due to the fact that lower cooling rate plays an important role in achieving the uniformity of temperature and composition in the remaining liquid, which is crucial to the formation of the spherical and homogeneous microstructure. However, a too low cooling rate will lead to a significant increase in grain growth time, which makes too coarse grains and more particles coalesce, so a certain abnormal growth of grain appears and the shape factor decreases slightly.

Numerical simulation on rheo-diecasting mould filling of semi-solid key-shaped component

Based on the experimental data of apparent viscosity about semi-solid A356 aluminum alloy, the apparent viscosity model was developed and inserted into a commercial software Castsoft6.0, and a key-shaped component filling process was simulated. The simulation results are in good agreement with the experimental filling results, which indicates that the apparent viscosity model established is effective and available. The process parameters on the cavity filling of the key-shaped components have been optimized. The injection pressure should be more than 15 MPa, the slurry flowing velocity in the in-gate should be more than 1.73 m/s, and the slurry temperature should be over 585 ℃.

Mechanical properties and microstructures of Al alloy tensile samples produced by serpentine channel pouring rheo-diecasting process

Abstract An innovative one-step semi-solid processing technique of A356 Al alloy, the serpentine channel pouring rheo-diecasting process (SCRC), was explored. The mechanical properties and microstructures of the tensile samples made by the SCRC technique were tested in the as-cast and T6 heat treatment conditions. The experimental results show that the as-cast ultimate tensile strength can reach about 250 MPa and the elongation is 8.6%-13.2%. The ultimate tensile strength can increase approximately 30% higher than that of the as-cast one but there is some slight sacrifice of the plasticity after T6 heat treatment. Under these experimental conditions, the semi-solid A356 Al alloy slurry with primary α 1 (Al) grains, which have the shape factor of 0.78-0.89 and the grain diameter of 35-45 μm, can be prepared by the serpentine channel pouring process. The primary α 2 (Al) grains are very fine during the secondary solidification stage. Compared with the conventional HPDC process, the SCRC process can improve the microstructures and mechanical properties of the tensile test samples. The advantages of the SCRC process include easily incorporating with an existing HPDC machine, cancelling the preservation and transportation process of the semi-solid alloy slurry, and a higher cost performance.

Preparation of semi-solid A380 aluminum alloy slurry by serpentine channel

Abstract The semi-solid slurry of A380 aluminum alloy was prepared by the serpentine channel. The effects of pouring temperature, curve number and curve diameter of the serpentine channel on the microstructure of the semi-solid A380 aluminum alloy slurry were investigated. The results show that the satisfactory semi-solid A380 aluminum alloy slurry could be obtained when the pouring temperature ranged from 630 to 650 °C. Under the same conditions, increasing the curve number or reducing the curve diameter of the serpentine channel would decrease the average diameter and increase the shape factor of the primary α (Al) grains. The “self-stirring” of the alloy melt in the serpentine channel was beneficial to the ripening of the dendrites and the spheroidizing of the primary α (Al) grains.

Rheo-squeeze casting of semi-solid A356 aluminum alloy slurry

Abstract The effect of pouring temperature, electromagnetic stirring power and holding process on semi-solid A356 aluminum alloy slurry was investigated, then the slurry was squeeze-cast. The results show that when the pouring temperatures are properly above the liquidus line, for example 630-650 °C, the slurry with spherical primary α (Al) grains can be prepared under the stirring power of 1.27 kW. The slurry is then homogeneously held for a short time, and the primary α (Al) grains are further ripened and distributed evenly in the slurry. The results of the rheo-squeezed casting experiments show that the injection specific pressure has a great effect on the filling ability of the semi-solid A356 aluminum alloy slurry, and the higher the injection specific pressure is, the better the ability for the slurry to fill the mould cavity is. When the injection specific pressure is equal to or above 34 MPa, the whole and compact rheo-squeezed castings can be obtained. The microstructure of the castings indicates that the shape, size and numbers of the primary α (Al) grains in different parts of the castings are highly consistent. After being held at 535 °C for 5 h and then aged at 155 °C for 12 h, the ultimate strength of the rheo-squeezed castings can reach 300-320 MPa, the yield strength 230-255 MPa, and the elongation 11%-15%.

Effect of trace Sn on corrosion behaviors of high voltage anode aluminum foil

The cube texture and the surface corrosion structure of aluminum anode foil for high voltage electrolytic capacitor containing trace Sn were investigated based on quantitative texture analysis and microstructure observation under SEM. High volume fraction of cube texture over 95% and obviously higher specific capacity are obtained in the foils with less than 0.002% Sn. It is indicated that the corrosion behavior of trace Sn on aluminum surface is similar with that of Pb. Higher content of Sn over 0.002% reduces the cube texture component and therefore the specific capacity. Sn, as an eco-friendly microelement, can be applied to replace Pb in improving the homogenous pitting behaviors of high voltage aluminum foils.

Preparation of semisolid A356 alloy slurry with larger capacity cast by serpentine channel

The integral microstructure of semisolid A356 alloy slurry with larger capacity cast by serpentine channel was studied and the influence of cooling ability of serpentine channel on the microstructure was investigated. The results indicate that ideal slurry with larger capacity can be prepared through serpentine channel with good cooling ability. When the serpentine channel was continuously cooled, both the longitudinal and the radial microstructure of the slurry was composed of granular primary phase and the integral microstructure uniformity of the slurry was good. However, uncooled serpentine channel can only produce larger slurry with fine grains in positions adjacent to its centre and with a large number of dendrites in positions close to its edge, thus, the radial microstructure of larger slurry is nonuniform. The pouring temperature is set up to 680 °C and the solid shell inside the channel can be avoided at this pouring temperature.