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The high fusion welding hot cracking sensibility of the next-generation alloy is the key technological difficulty that hinders its widely application in the aeronautic and astronautic industry. A critical review of the fusion welding hot cracking from the perspective of basic mechanism and the experimental research of typical materials was presented in this article. The fusion welding hot cracking phenomena include solidification cracking (occurs within the fusion zone) and liquidation cracking (occurs at the interface between fusion zone and partial melting zone). The formation factors of the fusion welding hot cracking include alloying composition, welding thermal cycle and thermal stress. Based on the comprehensive understanding of the formation mechanism of the fusion welding hot cracking, the relative research progress in the field of aluminum alloys, magnesium alloys, advanced high strength steel and nickel alloys was summarized. The establishment of the quantitative criterion that involves the effects of complicated multi-component and the morphology of the dendrite on the cracking sensibility is the key development direction. Optimizing the alloying composition of the base metal or filler metal, adding nucleanting agent or auxiliary facilities are the practical method for restraining the fusion welding hot cracking. Conducting the research on the mechanism and restraining method of the fusion welding hot cracking helps to solve the difficulty of the next generation alloys processing, which can realize their application in the field of aeronautic and astronautic industry.

With the improvement of alloy manufacturing level and the complexity of performance requirements, high-entropy alloys (HEAs) have gradually attracted great attention.At present,the research in the field of material processing mainly focuses on brazing and surface engineering.In the field of brazing, HEAs can be used as filler material for brazing at high temperature and low temperature, the empirical parameters related to high entropy were summarized. The application of the simulation and calculation methods such as first-principle method and calculation of phase diagram were described in the field of HEAs design for filler metals development. The latest research progress of HEAs fillers for brazing of nickel-based superalloys and dissimilar ceramics-metals, as well as low temperature packaging was introduced. The influence of welding process parameters on microstructure and properties of HEAs brazing joints was also analysed.In the field of surface engineering, the application direction and preparation methods of HEAs in film/coating were discussed. The research progress in high-temperature protective coating, hard protective layer and other application directions was summarized. At the same time, the problems existing in the research and application of HEAs in the fields of brazing and surface engineering were summarized. The future trends were put forward in order to decrease the melting temperature of HEAs filler, improve high temperature mechanical properties of welds, and develop the eutectic HEAs filler/coating.