Indirect Measurement of Material Thermal and Mechanical Properties during Welding

By means of a newly developed non-contact detecting method, electronic speckle pattern interferometry (ESPI), a method of determining material property data during welding is studied. A TIG fixed-point welding process is modeled in which some achievements of simulation, such as the effect of welding pool on temperature field and nonlinear relation between convection coefficient and temperature, are all considered. In addition, by taking into account effect of heating rate, the workpiece is divided into near-weld zone and far-weld zone, which will be treated with different property values. When the displacement field computed with original property data is compared and matched with the experimental displacement field, which is measured by ESPI, these original data are adjusted properly. A group of raw properties are obtained and are corrected by statistical regression before they enter the simulation process again.By such a loop of "simulation-comparison-modification", a set of property data that best satisfy the real condition are achieved finally. In such a way, a new method for measuring material properties during welding is found.

Microstructure and properties of AgCu/2 wt%Ag-added Sn-Pb solder/CuBe joints fabricated by vapor phase soldering

The purpose of this paper is to investigate the effect of 2 wt%Ag addition in Sn-Pb eutectic solder on microstructure and mechanical properties of AgCu/solder/CuBe joint fabricated by vapor phase soldering.63Sn37Pb and 62Sn36Pb2Ag solder pastes were used to join Cu(1.7 wt%-2.5 wt%)Be and Ag(2 wt%-5 wt%)Cu alloys.Two fracture modes are observed in 62Sn36Pb2Ag and 63Sn37Pb joints after lateral shear tests at room temperature or 120℃,and shear forces of 62Sn36Pb2Ag joints are far higher than those of 63Sn37Pb joints.No obvious difference is observed in morphology and thickness of intermetallic compounds(IMCs)at interfaces of the 63Sn37Pb and 62Sn36Pb2Ag joints.Within the two kinds of joints,for-mation of big blocky or plate-like Ag_(3)Sn is restrained.However,many Ag_(3)Sn IMCs particles(1-3 μm in width)in isolated and dispersed distribution are observed within 62Sn36Pb2Ag joints.The Ag3Sn particles are responsible for the better mechanical properties of 62Sn36Pb2 Ag joints than those of 63Sn37Pb joints.The results present in this paper may provide a guide for restraining formation of big blocky or plate-like Ag_(3) Sn in joints with Ag pads or thick Ag surface finish on pads by utilizing vapor phase soldering process,and improving mechanical properties of Cu/SnPb/Ag joints by adding Ag in SnPb eutectic solder.