Effect of B on microstructure and properties of joints brazed by In-situ Ag-Cu-Zn-Sn filler metal with high Sn content

The copper brazed joints were obtained by induction brazing using in situ synthetic high Sn content silver filler metals with different B contents and the effect of element B on the wettability of filler metals and microstructure and mechanical properties of the joints were studied. With the addition of element B, the spreading area of the filler metals on the copper increases. The microstructure of the joints mainly consists of silver-based solid solution and copper-based solid solution, and the distribution of silver-based solid solution in the brazing seam becomes dispersed with the addition of B. The width of the brazing seam increases significantly with the increase in B content. Meanwhile, the B element was mainly distributed in the Ag-based solid solution. The tensile strength firstly increased and then sharply decreased with B added. The maximum average tensile strength of 206.83 MPa was obtained with a 2% addition of B and the joint fracture pattern is a brittle fracture

Mechanism of oxide film removal by KF-AlF3 and CsF-AlF3 mixed fluxes on Cu and Al base metals and their effect on wettability

CsF-AlF3 was added in different mass percentages to KF-AlF3 flux, and CsF-AlF3/KF-AlF3 mixed fluxes with different components were prepared by ball milling. The melting curves of four kinds of fluxes were measured using differential scanning calorimetry (DSC). The properties of the fluxes were studied by flowing and wetting experiments. The intermetallic compounds (IMCs) at the interface of the filler metal/copper (Cu) base metal were studied by field emission scanning electron microscope (SEM-EDS), electron backscattering diffraction (EBSD). The results showed that as the mass of CsF-AlF3 increased, the solidus and liquidus temperatures of the flux gradually decreased. The flux has better flowability on the Cu and Al surfaces. In the presence of the fluxes, the wettability of the filler metal on the Al is better compared to the wettability on the Cu. Three kinds of IMCs, namely Cu9Al4, CuAl and CuAl2, were found at the interface between filler metal and Cu. The texture strength and deformation degree of CuAl2 with preferred orientation are the largest. The order of formation of IMCs is Cu9Al4, CuAl, CuAl2

Structure of Mpro from COVID-19 virus and discovery of its inhibitors

A new coronavirus (CoV) identified as COVID-19 virus is the etiological agent responsible for the 2019-2020 viral pneumonia outbreak that commenced in Wuhan. Currently there are no targeted therapeutics and effective treatment options remain very limited. In order to rapidly discover lead compounds for clinical use, we initiated a program of combined structure-assisted drug design, virtual drug screening and high-throughput screening to identify new drug leads that target the COVID-19 virus main protease (M). M is a key CoV enzyme, which plays a pivotal role in mediating viral replication and transcription, making it an attractive drug target for this virus. Here, we identified a mechanism-based inhibitor, N3, by computer-aided drug design and subsequently determined the crystal structure of COVID-19 virus M in complex with this compound. Next, through a combination of structure-based virtual and high-throughput screening, we assayed over 10,000 compounds including approved drugs, drug candidates in clinical trials, and other pharmacologically active compounds as inhibitors of M. Six of these compounds inhibited M with IC values ranging from 0.67 to 21.4 μM. Ebselen also exhibited promising antiviral activity in cell-based assays. Our results demonstrate the efficacy of this screening strategy, which can lead to the rapid discovery of drug leads with clinical potential in response to new infectious diseases for which no specific drugs or vaccines are available