Chun Zhang

Microstructure and properties of Al/Sip composites for thermal management applications

Aluminum matrix composite reinforced with high amount of Si particle is an advanced electronic packaging material used in thermal management. In this work, Al/Sip composites with different Si contents were prepared by rapid solidification and hot pressing. Fine and homogeneous microstructures with defect-free were achieved, and no detrimental reaction was detected. The typical thermo-physical properties such as the thermal conductivity and coefficient of thermal expansion (CTE) of the Al/Sip composites were acceptable as electronic packaging material for semiconductor devices. The CTE increased gradually with the temperature. Additionally, the mechanical properties of the composites were measured. The technological performance (workability, platability, and laser weldability) of the composites were also evaluated.

Thermal cycling reliability of Al/50Sip composite for thermal management in electronic packaging

Excellent thermal fatigue resistance with long-term reliability is one of the key requirements for thermal management materials. The effect of thermal cycling on mechanical properties and degradation mechanism of Al/50xa0wt% Sip composite are investigated. The composite is fabricated by hot pressing of pre-alloyed powder, and thermally cycled between room temperature and various temperatures (200, 250, and 300xa0°C) for up to 800 cycles. The results show that mechanical propertiesxa0of the composite are quite stable under the maximum heating temperature of 200xa0°C regardless of the number of thermal cycle. However, they decrease gradually under 250 and 300xa0°C with a greater number of thermal cycle. Microscopic observations indicate that the property degradation is mainly resulted from the fragmentation of Si particles owing to the thermal stress because of the coefficient of thermal expansion mismatch.

Effect of Particle Size on Microstructure and Cold Compaction of Gas-Atomized Hypereutectic Al-Si Alloy Powder

The effect of particle size on the cold compaction behavior of rapidly solidified hypereutectic Al-27xa0wtxa0pct Si alloy powder was studied by double action axial pressing at room temperature. The geometrical characteristics (morphology, size, shape, and distribution of Si reinforcing phase) and hardness of the powder as a function of the particle size were investigated. The result shows that finer powder particle size showed smaller primary Si particles and achieved a lower density at a given pressure. Whereas, the microhardness of Al matrix increases while the particle size decreases, which indicates that the supersaturation due to the high solidification rate increases the deformation resistance of the alloy powder. Furthermore, the geometrical characteristics of Si phases strongly depend on the particle size due to the suppressed growth of Si phases during atomization. This microstructural characteristic evidently affects the powder compactibility at high applied pressures.

Effect of pre-annealing on microstructure and compactibility of gas-atomized Al-Si alloy powders

Abstract Effect of pre-annealing treatment temperature on compactibility of gas-atomized Al-27%Si alloy powders was investigated. Microstructure and hardness of the annealed powders were characterized. Pre-annealing results in decreasing Al matrix hardness, dissolving of needle-like eutectic Si phase, precipitation and growth of supersaturated Si atoms, and spheroidisation of primary Si phase. Compactibility of the alloy powders is gradually improved with increasing the annealing temperature to 400 °C. However, it decreases when the temperature is above 400 °C owing to the existence of Si-Si phase clusters and the densely distributed Si particles. A maximum relative density of 96.1% is obtained after annealing at 400 °C for 4 h. In addition, the deviation of compactibility among the pre-annealed powders reaches a maximum at a pressure of 175 MPa. Therefore, a proper pre-annealing treatment can significantly enhance the cold compactibility of gas-atomized Al-Si alloy powders.

Reductive acid leaching of cadmium from zinc neutral leaching residue using hydrazine sulfate

Abstract Zinc neutral leaching residue (ZNLR) from hydrometallurgical zinc smelting processing can be determined as hazardous intermediate containing considerable amounts of Cd and Zn which have great threats to the environment. The ZNLR contained approximately 35.99% Zn, 15.93% Fe and 0.26% Cd, and Cd mainly existed as ferrites in the ZNLR in this research. Reductive acid leaching of ZNLR was investigated. The effects of hydrazine sulfate concentration, initial sulfuric acid concentration, temperature, duration and liquid-to-solid ratio on the extraction of Cd, Zn and Fe were examined. The extraction efficiencies of Cd, Zn and Fe reached 90.81%, 95.83% and 94.19%, respectively when the leaching parameters were fixed as follows: hydrazine sulfate concentration, 33.3 g/L; sulfuric acid concentration, 80 g/L; temperature, 95 °C; duration of leaching, 120 min; liquid-to-solid ratio, 10 mL/g and agitation, 400 r/min. XRD and SEM-EDS analyses of the leaching residue confirmed that lead sulfate (PbSO 4 ) and hydrazinium zinc sulfate((N 2 H 5 ) 2 Zn(SO 4 ) 2 ) were the main phases remaining in the reductive leaching residue.

Effect of individual and combined additions of Al–5Ti–B, Mn and Sn on sliding wear behavior of A356 alloy

Abstract The effect of grain refiner, Mn and Sn additions on the sliding wear behavior of A356 aluminum alloys was investigated. The microstructure and worn surfaces of the studied alloys were characterized by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The experimental results indicate that the alloy refined by Al–5Ti–B alloy exhibits equiaxed α(Al) dendrites and performs better wear resistance compared with the alloy without the grain refiner. Moreover, the addition of Mn can change the β-Al5FeSi phase to α-Al(Mn, Fe)Si phase and reduce the possibility of crack formation, thus improving the wear resistance. Sn added to A356 aluminum alloy forms Mg2Sn precipitates after heat treatment. Therefore, the unrealizable precipitation hardening Mg2Si phase and the softening β-Sn phase can reduce the hardness of the alloy, and finally reduce the wear resistance.

Effects of Mn and Sn on microstructure of Al–7Si–Mg alloy modified by Sr and Al–5Ti–B

Abstract The effects of Mn and Sn on the microstructure of Al–7Si–Mg alloy modified by Sr and Al–5Ti–B were studied. The results show that the columnar dendrites structure is observed with high content of Sr, indicating a poisoning effect of the Al–5Ti–B grain refinement. In addition, Sr intermetallic compounds distribute on the TiB 2 particles, which agglomerate inside the eutectic Si. The mechanism responsible for such poisoning was discussed. The addition of Mn changes the morphology of iron intermetallic compounds from β -Al 5 FeSi to α -Al(Mn,Fe)Si. Increasing the amount of Mn changes the morphology of α -Al(Mn,Fe)Si from branched shape to rod-like shape with branched distribution, and finally converts α -Al(Mn,Fe)Si to Chinese script shape. The microstructure observed by transmission electron microscopy (TEM) shows that Mg is more likely to interact with Sn in contrast with Si under the effect of Sn. Mg 2 Sn compound preferentially precipitates between the Si/Si interfaces and Al/Si interfaces.

Characterization of Rapidly Solidified Al-27 Si Hypereutectic Alloy: Effect of Solidification Condition

Rapidly solidified Al-27wt.%Si hypereutectic alloy was fabricated by gas atomization, and its characterization as a function of particle size was investigated. A relationship between the particle size and solidification condition was established to understand the microstructural characteristics. While the irregular primary Si phase transformed to quasi-spherical shape, and its size decreased gradually with the particle size, the primary Si morphology similar to that in ingot metallurgy sample was found from the deep-etched images. In the fine powder, the eutectic Si phase formed a network structure densely distributed in the matrix, while a tangled dendritic formed at the surface. From the distribution of the Si phase, it is suggested that the microstructure inhomogeneity increased as the particle size decreases. The structural distortion of the Al matrix was observed from x-ray diffraction patterns and differential scanning calorimetry curves. From the calculated results, an undercooling of 33xa0K (or interface velocity of 8xa0mm/s) was sufficient to suppress the primary Si to less than 2xa0μm in the present composition. The microhardness increased significantly while the particle size decreases. The microstructure and properties of the bulk material consolidated by hot pressing of the powders obtained were also conducted.

Stabilization of Heavy Metal Containing Smelting Ash through Mechano-Chemical Reaction

The present study described the application of mechano-chemical reaction on stabilization of heavy metal containing smelting ash. Extraction procedure for leaching toxicity test showed that the leaching toxicity of cadmium and lead in smelting ash decreased very significantly after grinded. The optimal condition of the mechano-chemical stabilization process was established as follow. The ball milling medium was stainless steel, the additive was the mixture of elemental sulfur and iron powder, the dosage of additive was n(Cd):n(Fe):n(S)=1:3:3, and ball milling time was 3.5 hour. The results showed that the leaching toxicity of cadmium decreased from 2496 mg/L to 0.43 mg/L, compared to lead decreased from 7.30 mg/L to 0.12mg/L under the optimal condition.

Enhanced cadmium extraction from zinc neutral leaching residue using sulfur dioxide

Enhanced reductive leaching of cadmium from zinc neutral leaching residue, along with zinc and iron, was conducted using sulfur dioxide as reductant. Cadmium mainly exists as cadmium-bearing zinc ferrite (CdxZn(1-x)Fe2O4) (x = 0~1). The influence of variables on the extraction rates of cadmium, zinc, and iron was studied. The results showed the maximum extraction of cadmium, zinc, and iron reached 99.11%, 93.43%, and 93.38% under the optimum conditions. The raw and the reductive leaching residue were characterized by XRD, ICP, and SEM-EDX analysis. Lead sulfate, zinc, and cadmium sulfide are the main phases contained in the reductive leaching residue.