Papers by Author: Qi Ming Dong

Abstract: Two kinds of thick-walled rings, consisted of WCP/Fe-C gradient composites layers containing about 54 and 70 vol.% of WCP and Fe-C alloy core, were cast by centrifugal casting method. The microstructure, mechanical properties and wear resistance of the gradient composites were investigated. Meanwhile the results were compared with those made of the high speed steel. It was found that WCP in the two kind of gradient composites layers were even well distributed, WCP/Fe-C composites layer of 23-28mm was obtained, the transition layer between the composites layer and matrix alloy core was perfect. The tensile strengths of the two gradient composites layers achieved 345MPa, 460MPa and the impact toughness were 4.6J/cm2, 6.2J/cm2 respectively. Moreover the hardness of the composites layers attained HRA81 and HRA 78. The result of the comparison among the gradient composites layers and that made of the high speed steel showed that the wear resistance of the gradient composites layers containing about 50 and 70 vol.% of WCP was more than 20 times higher than that of the high speed steel under loads of 100N and 200N and sliding velocity of 60 m/s. Finally, the wear-mechanism was discussed.

Abstract: The aging process of lead frame Cu-Cr-Sn-Zn alloy has only been studied empirically by trial-and-error method so far. This paper builds up the prediction model of the aging properties via a supervised artificial neural network(ANN) to model the non-linear relationship between parameters of aging process with respect to hardness and electrical conductivity properties of the alloy. The improved model is developed by the Levenberg- Marquardt training algorithm. The predicted values of the ANN coincide with the tested data. So the ANN system is effective and successful for predicting and analyzing the properties of Cu-Cr-Sn-Zn alloy. The optimized processing parameters are available at 475 C ° -520 C ° aging for 2h-1h.

Abstract: By using the finite element method and large strain two-dimension plane strain model, the flaking damage of Cu-Fe-P lead frame sheet is investigated. The characterization of microstructure under surface flaking is the larger Fe particles embedded in the copper matrix. The numerical analysis reveals that at the interface of Cu and Fe there are greater strain mutation and intense stress concentration that is increased with particle diameter and the extent of deformation. This strain and stress concentration makes the interface initiate crack and develop crack easily. The micro-crack around the Fe particle is also attributed to surface flaking damage under the finish rolling deformation. The larger Fe particles should be avoided in the production of Cu-Fe-P alloy.

Abstract: Milisecond high density electrical pulse was used to age one of the typical IC lead frame materials Cu-2.5Fe-0.03P-0.1Zn copper alloy. The effects of electrical pulse aging on the microstructures, electrical conductivity and microhardness of this alloy were systematically investigated. The experimental results shown that the alloy phase precipitated in Cu-2.5Fe-0.03P-0.1Zn copper alloy during electrical pulse aging could be controlled to the order of nano-size and the ideal match of electrical conductivity and microhardness could be achieved in the condition of optimized parameters of electrical pulse. The electrical conductivity of the alloy was kept at above 60%IACS while the microhardness reached to HV115. A preliminary theoretical analysis was made to explain the unique action of electrical pulse.

Abstract: Effects of the mold rotating speeds on the gradient microstructure and properties of heavy cross-sectional WCP/Fe-C composites made in a self-made centrifugal machine have been investigated with SEM, EDS etc. The results show the ring sample of WCP/Fe-C composites made in a centrifugal machine was free of any defects. And the transition layer between the working layer of WCP/Fe-C composites and matrix Fe-C alloy core was also perfect. The experimental results also show that the WCP-radius-directional distribution in the composites was a continuous component gradient one, which was changed with the various mold rotating speeds. At 1000 rpm the volume fractions of the WC particle from outer layer to inner layer were about 70 vol% to 50 vol% and, at 1400 rpm the volume fractions were about 80 vol% to 65 vol% respectively. The hardness and impact toughness of the working layer of WCP/Fe-C composites were changed with increasing of the mold rotating speeds respectively. Finally, the mechanism of the effects of the mold rotating speeds was discussed in the paper.

Abstract: Al2O3 dispersion strengthened copper composite (Al2O3p/Cu composite) was produced by internal oxidation. The hardness and electrical conductivity of the produced Al2O3p/Cu composite (0.60 wt.% Al2O3) subjected to high temperature annealing treatments after different cold work deformations have been investigated; the microstructures of the composite have also been analyzed by TEM. Results show that the microstructure of the composite is characterized by an uniform distribution of nano-Al2O3 particles in Cu-matrix; the composite can maintain more than 91% hardness retention after 1h, 1000°C annealing treatment; the recrystallization of the Cu-matrix can be largely retarded and only partially happened even annealing for 1h at 1050°C, following cold deformation of 84%.