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Nitrile rubber O-rings seals for packaging barrel was stored in China tropical marine atmosphere environments for 10 years, and then the sealing function of nitrile rubber O-ring was failed. By comparing the molecular structure, cross-link density, thermal decomposition, content of elements and chemical functional groups of the original nitrile rubber seals, the surface and interior of nitrile rubber seals storage for 10 years, a long-term natural failure mechanism was studied. The results showed that: the surface content of dibutyl phthalate and dibutyl sebacate, the surface carbonyl peak height and the surface content of oxygen element were higher than that in internal; the surface cross-link density was lower than that in internal but still higher than in original sample; and surface carbon- to-oxygen ratio were lower than that in internal and original sample. After aging for 10 years, the weight loss of plasticizer decreased, and the main chain content increased. It can be inferred that nitrile rubber mainly undergoes oxygen-absorbing cross-linking reaction to form carboxylic acids and esters, which is accompanied by the migration and enrichment of two plasticizers to the surface, causing reductions in elasticity and elasticity. The residual permanent compression set was lower than the design critical value, and the sealing function for the packaging barrel was lost, and a leak occurred.

Welding-brazing method is widely used for dissimilar metals welding. However, it is becoming increasingly difficult to further improve the connection strength by controlling the formation of the transition layer. In this study, an innovative welding method referred to as adjacent welding was addressed, which greatly improved the tensile strength of Ti/Cu dissimilar joint. The strength of new joint could reach up to 89% that of copper base metal, compared to the use of a traditional welding-brazing method which strength coefficient is within the limit of 70%. In order to determine the strengthening mechanism of adjacent welding, optical microscopy, SEM, EDS and XRD were applied for the analysis of microstructure and phase structure. Furthermore, tensile strength was also tested. The results show that due to the process of remelting and reverse solidification of intermetallic compounds (IMCs) layer, a less complex and thinner IMCs layer was formed and TiCu (553 HV) with high embrittlement existing in the front of titanium substrate was changed into Ti2Cu (442 HV). Performances of joints were optimized by these changes. An interpretation module was presented for the mechanism. Keywords: Welding-brazing, Adjacent welding, Dissimilar welding joints, Intermetallic compounds

Copper (T2) and 304stainless steel were joined by EBW with different beam offset. Full-strength joint as well as the offset joints of sufficient strength can be obtained. The highest tensile strength reaches 250Mpa, which is almost equal to the strength of copper. By analyzing phase structure and distribution of weld zone, bonding interface of fusion zone, width and grain size of heat affected zone, diffusion behavior of Fe/Cr, cooling rate and fracture behavior, the effect of beam offset on the joint strength was detailed studied. The results show that beam offset is flexible and allowed to be in the range of −0.2 mm to 1 mm. Under the condition of small beam offset, the performance of the joint is nice because of narrow HAZ and weld zone of few defects. But for large offset which leads to low joint performance on copper side or steel side, the main reasons respectively are deterioration of HAZ, FZ and low metallurgical bonding of root interface. Toughness fracture was proved by dimples for fusion welding, but brittle fracture occurred for re-melt deposit welding of large offset.

Under the background of lightweight design, manufacturing and improvement of comprehensive performance, dissimilar metals connection has been becoming a research focus recently and will have a broad application prospect. Titanium alloy TC4 and 304 stainless steel have many excellent properties, achievement of effective connection between these two materials has a significant promoting effect on Industrial Technology. However, the bonding connection of TC4/304 is very poor, so it is necessary to redesign the joint and further study the strengthening mechanism. In the paper, connection experiment of TC4/304 was carried out using two methods: Electron Beam Welding and Friction Stir Welding. Optical microscopy, SEM, EDS were applied for the analysis of microstructure and phase structure. The results state that EBW and FSW are effective and the maximum strength are 196 Mpa and 178 Mpa respectively. Both failure mode are brittle fracture.