Shanghai Key Laboratory of Materials Laser Processing and Modification

Shanghai, China

Shanghai Key Laboratory of Materials Laser Processing and Modification

Shanghai, China

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Yu C.,Shanghai JiaoTong University | Yu C.,Shanghai Key Laboratory of Materials Laser Processing and Modification | Yang Y.,Shanghai JiaoTong University | Lu H.,Shanghai JiaoTong University | And 3 more authors.
Journal of Electronic Materials | Year: 2010

Kirkendall voids (KVs) are known to be formed at the Cu/Cu 3Sn interface, which can remarkably weaken solder joints. In this paper, the formation and evolution processes of KVs at Sn-3.5Ag/Cu joints were systematically investigated under isothermal aging and current stressing. It was found that the processes develop faster when joints are subjected to current stressing as opposed to thermal aging. This can be illuminated by the high KV densities caused by current stressing at both cathode and anode Cu/Cu 3Sn interfaces. Moreover, KVs formed under current stressing showed some polarity characteristics, namely that higher KV density was observed on the anode side compared with the cathode side. The interfacial reaction generated at the Cu 3Sn/Cu 6Sn 5 interface, which was partly affected by current stressing, contributed to this polarity effect. As the holding time was prolonged, microvoids coalesced into larger porosities and microcracks. These defects will greatly threaten the reliability of the interface. © 2010 TMS.


Yao C.,Shanghai JiaoTong University | Yao C.,Shanghai Key Laboratory of Materials Laser Processing and Modification | Xu B.,National Key Laboratory for Remanufacturing | Huang J.,Shanghai JiaoTong University | And 5 more authors.
Optics and Lasers in Engineering | Year: 2010

Softening in overlapping passes by laser-overlapped scanning surface hardening is a difficult problem of laser surface modification. Despite the advantage of laser quenching, softening in overlapping zone limits its practical application. In this paper, 45, 9Cr2Mo and W18Cr4V steel were hardened by laser-overlapping quenching. Softening occurred in all overlapping zones. The results of hardness testing indicated the softening width of 45 steel was the broadest and that of W18Cr4V steel was the narrowest. Different mixed microstructures composed the overlapping zone for three steels, i.e., tempered sorbite and a little tempered martensite in 45 steel, tempered martensite, tempered sorbite and a small amount of carbides in 9Cr2Mo steel, tempered martensite and a little carbide in W18Cr4V steel. The effect of activation energy of diffusion for carbon in steel and cooling rate on the decomposition of martensite have been investigated by developing a diffusion model based on the principle of carbon diffusion in martensite. The results indicated that action energy for diffusion of carbon in steel plays a main role in hindering decomposition of carbide and cooling rate has a limited action in reducing temper softening during laser-overlapping scanning. © 2009.


Gao Z.,Shanghai Key Laboratory of Materials Laser Processing and Modification | Gao Z.,Shanghai JiaoTong University
Applied Mechanics and Materials | Year: 2010

In order to better understand heat transfer and fluid flow pattern in the weld pool of lasermetal inert gas (MIG) hybrid welding aluminum-alloy process, weld formation mechanism and weld pool dynamic behavior were analyzed by a three-dimensional mathematical model for moving laser- MIG hybrid welding. The temperature and velocity distribution of weld longitudinal section for laser-MIG moving hybrid welding at different moment were discussed to explain flow dynamic behavior in the weld pool. In addition, weld formation mechanism was illustrated by a transverse section heat history evolvement. Moreover, the effects of laser welding parameter and MIG welding parameter on important weld geometry characteristic were quantitatively studied using the mathematical model, and the simulated weld bead geometry parameters were in good agreement with experimental measurements. © (2010) Trans Tech Publications.


Yu C.,Shanghai JiaoTong University | Yu C.,Shanghai Key Laboratory of Materials Laser Processing and Modification | Chen J.-S.,Shanghai JiaoTong University | Wang K.-Y.,Shanghai JiaoTong University | And 3 more authors.
Journal of Materials Science: Materials in Electronics | Year: 2013

Cu3Sn intermetallic compound (IMC) layer is usually formed in solder joints. Since the formation of Cu3Sn could induce large volume shrinkage, and further cause a lot of reliability issues, many works focused on suppressing the formation or growth of the Cu3Sn layer. This work explored that Cu and Ag alloying elements also have benefit in suppressing the Cu3Sn growth during isothermal aging stage. The Cu6Sn 5 IMC layer seems to be much stable in the Sn/Cu solder joint during aged at 150 and 180 C, its thickness changed little, while the Cu3Sn IMC layer grew much quickly. After about 300 h, the thickness of Cu 3Sn layer exceeds that of Cu6Sn5 layer. For the Sn-3.5Ag/Cu and Sn-0.7Cu/Cu solder joints, the thickness of Cu3Sn layer is near half of that of Cu6Sn5 layer. According to the relation between interface location and aging time, the reaction generated at the Cu6Sn5/Cu3Sn interface, which is governed by atom fluxes, controls the growth of Cu3Sn IMC layer. Since Ag and Cu alloying elements suppress the coarsening of Cu 6Sn5 IMC grains, the diffusion paths for Cu atoms toward the solder are more for Ag or Cu containing solder joints. Therefore, the growth of the Cu3Sn layer by consuming Cu6Sn5 layer is slower in the SnAg/Cu and SnCu/Cu solder joints than that in the Sn/Cu joints. © 2013 Springer Science+Business Media New York.


Yao C.,Shanghai JiaoTong University | Yao C.,Shanghai Key Laboratory of Materials Laser Processing and Modification | Huang J.,Shanghai JiaoTong University | Huang J.,Shanghai Key Laboratory of Materials Laser Processing and Modification | And 6 more authors.
Applied Surface Science | Year: 2011

An investigation is reported on crack-free laser clad Fe-based alloy by use of biaxial powder feeding shielded with argon gas. The microstructure and phase structure of the coating were studied, and mechanical properties were analyzed through hardness, tension strength and wear resistance of the coating. Microstructure analysis showed that there was retained austenite with spherical particles distributed therein in the interdendritic and nearby grain boundary regions. The mechanical test results showed that net-like distributed retained austenite in the interdendritic region had certain toughening effect through blunting crack-tip. Under wear condition of high sliding speed and high loading, the wear resistance of the coating with net-like retained austenite was much higher than that of the coating with some discontinuous carbide network or carbide blocks. The results showed that toughening of laser clad Fe-based alloy with high hardness over 850 HV could be achieved by modifying interdendritic phases from net-like carbide to net-like austenite with spherical particles. © 2010 Elsevier B.V. All rights reserved.


Yu C.,Shanghai JiaoTong University | Yu C.,Shanghai Key Laboratory of Materials Laser Processing and Modification | Yang Y.,Shanghai JiaoTong University | Li P.,Shanghai JiaoTong University | And 4 more authors.
Journal of Materials Science: Materials in Electronics | Year: 2012

Kirkendall voids (KVs) have disastrous effects on the properties of the solder joints in the integrated circuits, which are formed after the occurrence of the Cu 3Sn intermetallic compound (IMC) layer at the Sn-based solder/Cu interface. In this paper, 0.1 and 0.3 wt% Ge additions were separately added into the Sn-3.5 wt%Ag eutectic solder, to investigate the effects of Ge on the interfacial reaction under thermal aging at 150 °C. It is found that the Cu 6Sn 5 layer was still the original product, regardless of the concentration of Ge. Moreover, Ge was identified to dissolve into the IMC layer. As the aging time was prolonged to 10 days, the concentration of Ge increased to about 3.0 at%, but the Cu 3Sn IMC layer was not obvious. The single Cu 6Sn 5 IMC layer became flat little by little. Meantime, the thickness of the IMC layer increased slowly. And more significant finding is that the KVs were also not obvious at the interface. © 2011 Springer Science+Business Media, LLC.


Wu Y.,Shanghai JiaoTong University | Wu Y.,Shanghai Key Laboratory of Materials Laser Processing and Modification | Cai Y.,Shanghai JiaoTong University | Cai Y.,Shanghai Key Laboratory of Materials Laser Processing and Modification | And 4 more authors.
Journal of Materials Processing Technology | Year: 2015

By matching with the welding speed, the distance between the laser focus and butt seam was adjusted to obtain various fusion ratios of the two base metals. The main phases in weld metal were martensite and retained austenite whose proportions and morphology were measured by XRD and EBSD, respectively. The proportion of retained austenite, both at grain boundary and among martensite laths in core region of grain, increased with the fusion ratio of SUS304. The maximum content of retained austenite at grain boundary and in core region of grain could reach about 22% and 5.8%, respectively. The low-temperature impact toughness of the joint was improved with the increment of retained austenite content. The low-temperature impact energy at -196 °C had displayed a significant raise from 15 J to 44.3 J. The corresponding impact fracture section also transformed from cleavage fracture to entirely ductile fracture. © 2015 Elsevier B.V. All rights reserved.


Yu C.,Shanghai JiaoTong University | Yu C.,Shanghai Key Laboratory of Materials Laser Processing and Modification | Yang Y.,Shanghai JiaoTong University | Wang K.,Shanghai JiaoTong University | And 6 more authors.
Journal of Materials Science: Materials in Electronics | Year: 2012

Several different kinds of intermetallic compound (IMC) layers were fabricated through adding trace elements into the Sn-3.5Ag solder, to investigate the relationship between the Kirkendall void (KV) and the IMC layers. The results show that a considerable amount of KVs were observed at the Cu 3Sn/Cu interface in the Sn-3.5Ag/Cu joint after isothermal aging. A proper amount of Zn (0.5 wt%) and Ge (0.1 and 0.3 wt%) were found to effectively suppress the formation of the Cu 3Sn layer, and no obvious KVs were observed at the Cu 6Sn 5/Cu interface, while more Zn induced the formation of the Cu 6Sn 5 plus Cu-Zn mixed IMC layer, and voids (not KVs) were observed at the Cu 6Sn 5/Cu-Zn interface. (Cu,Ni) 6Sn 5 IMC layer replaced the initial Cu 6Sn 5 at the SnAg-Ni/Cu joints, likewise, the Cu 3Sn was suppressed at the thermal aging stage. Moreover, voids were found at the IMC/solder interface, while not at the IMC/Cu. Therefore, the formation of KVs is greatly determined by the characteristic of the IMC layer, this is consistent with the previous reports. On other hand, the KV can be suppressed by controlling the interfacial phase through adding trace elements into the solder. © 2011 Springer Science+Business Media, LLC.


Wu Y.,Shanghai JiaoTong University | Wu Y.,Shanghai Key Laboratory of Materials Laser Processing and Modification | Cai Y.,Shanghai JiaoTong University | Cai Y.,Shanghai Key Laboratory of Materials Laser Processing and Modification | And 4 more authors.
Materials and Design | Year: 2015

The dissimilar joints between SA553 and SUS304 were produced by CO2 laser welding with the ERNiMo-8 and ER308L filler wire. After welding parameters were optimized, qualified weld formations were made. Investigation on the microstructure showed that there were dual phases (martensite and austenite) in the ER308L weld, but only austenite in the ERNiMo-8 weld. For both joints, not only the microstructure gradient, but also the element gradient was observed near interfaces between weld metals and base metals. The Charpy impact and tensile test at room (25°C) and low temperature (-196°C) was implemented. The cryogenic impact energy of the ER308L weldment was 51J, lower than the value (84J) of the ERNiMo-8 weldment. The corresponding cryogenic tensile strength of the two weldments was 1070MPa and 960MPa, respectively. The cryogenic tensile properties of both weldments were rather higher than requirements in the relevant standards. The ERNiMo-8 weldment showed relatively better comprehensive performance when the cryogenic toughness was considered. © 2015 Elsevier Ltd.


Sun J.,State Key Laboratory of Development and Application Technology of Automotive Steels | Sun J.,Shanghai JiaoTong University | Sun J.,Shanghai key Laboratory of Materials Laser Processing and Modification | Yan Q.,State Key Laboratory of Development and Application Technology of Automotive Steels | And 5 more authors.
Materials and Design | Year: 2016

Butt joining of AA6061 aluminum alloy and Q235 low-carbon steel of 2.5mm thickness was conducted using laser welding-brazing method with ER4043 filler metal. An electro-galvanizing process of the steel was performed to obtain a zinc coating at the steel's bevel surface before welding. The brazing interface and the tensile strength of the joints were evaluated. The results showed that a sound butt joint between Al and steel was obtained, with the brazing interface consisted of zinc rich regions and a Fe-Al intermetallic (IMC) layer. The thickness and morphology of the IMC reaction layer were not constant but varied along the brazing interface. The morphology of the IMC reaction layer was more complex and the layer was thicker when a smaller bevel angle of the steel was used. All the joints fractured in the Fe2Al5 layer of the brazing interface. The tensile strength of the joints was mainly determined by the bonding area of the brazing interface, and average tensile strengths of 110MPa and 150MPa were achieved when bevel angles of 45° and 30° were used respectively. © 2015 Elsevier Ltd.

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