Materials Science Forum Vols. 475-479

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: Two major challenges in relation to laser welding are abrupt change in metallurgical aspects and actual assessment of the mechanical properties due partly to very narrow heat affected zone (HAZ) and partly to high mechanical properties gradient. The rapid thermal cycle of laser welding imposed on the HAZ was physically simulated using a Gleeble™ dynamic simulator equipped with a special isothermal quenching device (ISO-Q™), and a relatively large volume of HAZ with a homogeneous microstructure was obtained. The thermal cycles were determined from actual laser welding followed by laser tempering. Estimations of microstructure and mechanical properties of the simulated HAZs of an ultrafine grain steel imposed by laser welding with or without post-weld laser tempering were performed. The results indicate that the simulated HAZs, depending on the thermal history, are composed of lathy martensite with different pocket size and dislocation density. The impact toughness of as-welded HAZ is improved in contrast to the base material, but is further degraded by a following laser tempering, which, however, alleviates the abrupt change in hardness of as-welded HAZ.

Abstract: A method to predict the solid-liquid interface stability and the constrained dendrite growth of multi-component alloys was developed based on the Calphad method. The method was applied to several industrial Al-Si-Mg alloys, and the predicted results were compared with some former experimental data. The good agreement between the calculation results and the experimental data demonstrates the superiority of the present method to the classical one based on constant parameter assumptions.

Abstract: By using data of Curved Wide Plate (CWP) tests, a simple procedure to derive tolerable girth weld defect sizes is presented. The procedure involves prediction of the maximum tolerable defect size as a function of the applied remote plastic strain and the actual pipe and weld metal properties. Application of the methodology requires a reliable non-destructive testing technique that can detect the critical defect dimensions.

Abstract: Multiple defects in welds, when detected, have to be assessed for interaction. Current code rules are based on linear elastic fracture mechanics whereas the failure mode for welds in thin structures is primarily plastic collapse. Results of large-scale tests illustrate that current interaction rules have a high degree of conservatism for plastic collapse conditions. Guidance for the assessment of defect interaction under plastic collapse is proposed.

Abstract: We present results on microwave and millimeter-wave processing of materials. The research is primarily based on two systems– a 2.45 GHz, 6 kW S-band system and an 83 GHz, 15 kW gyrotron based quasi-optical system. These systems have been used for a wide range of material processing experiments. We describe the capabilities of these systems and discuss some of the results, including nanophase material production, rapid sintering, coating removal and joining of high temperature ceramics.

Abstract: In the last two decades copper metallurgy has faced tough challenges to comply with environmental regulations and falling copper prices. Although in the last months copper price has increased, still the environmental issue and operation related costs remain and as long as foreseen they will continue to do so. To reduce emissions to the atmosphere and to shorten the converting cycle, most industrial processes, as well as emerging ones, are aiming at production of high matte grade. However, the increase in oxygen potential required by these processes results in highly oxidised slags with significant copper contents, which require their treatment for copper recovery. Despite the fact that long established slag cleaning processes perform reasonaby well for slags in the range 1.5% - 2.5% in copper, i.e. coexisting matte in the order 60% in copper content, they must be reconsidered when applying to slags equilibrating with high matte grades and/or white metal. The present study concentrates on the mechanism of copper losses into slags, its association to sulfur and oxygen, mainly, and methods for its recovery. Based on these considerations, high temperature liquid-liquid phase separation, i.e. Teniente type reactor, slag flotation and slag leaching methods technologies are discussed as specially applied in Chilean smelters. Also, a new approach based on material characteristics of both matte and slag, i.e. magnetic separation, is presented.

Abstract: Mold filling characteristics in the Mg Expendable Pattern Casting(EPC) process were investigated in terms of casting conditions such as reduced pressure, pouring temperature and casting modulus including foam materials. With increasing pouring temperature up to 775oC the filling velocity increased. However, the filling velocity decreased at temperatures above 775oC. This is likely due to the increase of back pressure. Concerning the effect of reduced pressure on filling velocity, it increased sharply at lower reduced pressure while became stable at higher reduced pressure. In thick pattern, high reduced pressure would be needed to obtain high filling velocity. In expanded polystyrene(EPS) patterns, mold filling was found to be faster in the thick pattern than thin pattern at temperatures below 750oC. This propensity was observed to be reverse at pouring temperatures above 750oC. In polymethyl methacrylate(PMMA) patterns, the filling velocity almost leveled off without showing a dependence of pouring temperature. This result is attributed to the difference in gas pressure between EPS and PMMA patterns during the EPC process.