Abstract: The effect of adding Bi to a eutectic Sn-3.5Ag solder alloy on the growth kinetics of the intermetallic compounds (IMCs) in solder/Cu joints was examined at the aging temperatures of 130°C, 150°C and 180°C. At 150°C and 180°C, the growth rate of the Cu6Sn5 layer was significantly enhanced, but that of the Cu3Sn layer was rather reduced with increasing Bi content up to 12 wt.%. At 130°C, however, both the η and ε layers appeared to grow faster as the Bi content in the solder was increased to 12 wt.%. These results suggest that the accumulation of Bi ahead of the Cu6Sn5 layers can affect not only the interfacial reaction barrier but also the local thermodynamics at the interface between the Cu6Sn5 layer and the solder.
Abstract: Previous works have shown that a minimum yield strength s0 of 58 MPa for leadcalcium- tin anodes of 6 mm thickness and a nominal composition of 0.7% Ca and 1.3% Sn are required to avoid early deformations and distortions during their operation in copper electrowinning cell. This s0 value for the anodes is associated with a terminal cold rolling process and a further precipitation hardening prior to their installation in the electrowinning cells. The objectives of the present work are to determine the alloy recrystallization temperature according to Ca and Sn contents, the maximum cold rolling temperature and the aging time required to obtain the desired mechanical quality. The results indicate that recrystallization temperature ranges between 120 and 150°C, according to the anode composition. To reach the desired deformation and precipitation hardening and consequently a yield strength of 58 MPa, the maximum cold rolling temperature is 45°C and the minimum aging time, 30 days.
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: Titanium and titanium alloys have low density, high strength, excellent corrosion resistance in many media and are known to be biocompatible. This combination of properties makes titanium and its alloys an excellent choice for the applications, such as watch parts, medical devices, dental parts and sports goods. However, in the respect of fabricating complicated shaped parts, low machinability may be a barrier to practical uses. Therefore, it is considered to be very available that metal injection molding(MIM) process is applied to fabricate titanium alloy parts[1-2].
Nevertheless, injection molding of titanium and its alloys presents a real challenge to the processor due to its reactivity. Titanium not only has a strong affinity to oxygen, but also tends to react readily with carbon, nitrogen or hydrogen from the furnace atmosphere. Therefore, contamination by interstitial light elements such as oxygen and carbon is a serious problem because they have much influence on the mechanical properties of titanium alloys[3-5]. So it is necessary to control debinding and sintering conditions. In this paper, preparation of Ti-6Al-4V compacts was performed by MIM process. To reduce the contamination, the debound compacts were sintered at moderate temperature range from 1170°C to 1320°C and high vacuum (10-3Pa). On these conditions, the mechanical properties and relative
density of sintered compacts were investigated.
Abstract: Interface morphology and solute partition during directional solidification process of
Al-1.5Cu-3.0Zn alloy were investigated at temperature gradient of 80K/cm and growth rate between 0.1 and 7.1µm/s. The solid-liquid interface was quenched during directional solidification and the micromorphology at the longitudinal section was examed by optic microscope and SEM. The cellular growth interface and dendritic growth interface were observed and characterized. The distribution of
Cu and Zn was measured by EDS, the equilibrium solute partition coefficients for Cu and Zn in Al-1.5Cu-3.0Zn alloy were obtained to be 0.31 and 0.58. The activity model and concentration model, developed by present authors, were used to calculate the equilibrium solute partition coefficients in Al-1.5Cu-3Zn alloy. The model-calculated results were compared with experimental data.
Abstract: In this study, the distribution of electromagnetic pressure and the coupling between
shaping force and temperature field are investigated in electromagnetic contactless shaping process for plates of stainless steel and superalloy. The distributions of electromagnetic pressure on outlines of melt cross sections are very different along sides than at corners. Under the vacuum, the cooling ability is not strong enough, and therefore the position of melt in inductor is too low, which causes an unbalance between electromagnetic pressure and static pressure. Experiments show the insert of a screen shell from the bottom of inductor can change the distribution of magnetic field very much and make a good and stable coupling between shaping force and temperature field.
Abstract: Microstructural evolution of bulk undercooled Ni-40wt%Pb hypermonotectic alloy was systematically investigated by using molten glass purification and superheating cycling. Within the achieved undercooling range, the microstructures were classified into three categories. When the undercooling was less than 50K, the microstructure consisted of coarse dendritic grain and interdendritic Pb lumps. Increasing undercooling to the range 100 to 198K, macrosegregation was serious. When the undercooling was up to 292K, refined granular grain with homogeneously distributed fine Pb particles on it formed. The granulation mechanism of granular grains was owing to dendritic disintegration and subsequent recrystallization.
Abstract: The failure of flip chip solder joints through the dissolution of the Cu metallization was
studied. From the location and geometry of the dissolved Cu, it can be concluded that current crowding played a critical role in the dissolution. It can also be concluded that temperature, as an experimental variable, is not less import than the current density in electromigration study. Experimentally, no evidence of mass transport due to thermomigration was observed.
Abstract: This paper describes the effect of the interrelation between the base and weld metal postyield characteristics on the CMOD (Crack Mouth Opening Displacement) and the straining capacity of a defective weld. The effect is discussed and illustrated by means of test data obtained from standard CTOD and tension loaded wide plate tests.
Abstract: Despite many years of research, an understanding of the effect of misalignment is far from complete. This study is focused on an experimental assessment of the interaction between high-low misalignment (hi-lo) and defect tolerance of girth welds subjected to remotely applied plastic strains. The paper highlights the beneficial effect of weld strength overmatch on straining capacity and inherent conservative assumptions made in a standard ECA analysis.