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The grey irons prepared by adding steel scrap as main raw material were designed. Effect of the steel scrap content on the microstructures, mechanical properties and fracture mechanisms of the HT250 grey irons was studied. The results show that as the steel scrap content increased, the microstructures of the grey irons are improved, and the mechanical properties of the grey irons are therefore increased. The grey iron by adding 100 wt-% steel scrap has the optimal microstructure composed of the small and curved graphite flakes, the refined pearlite colonies and the dispersed MnS and TiN inclusions, also, it has the highest mechanical properties and comprehensive performance.

The paper focused on the changes in microstructure and mechanical properties of the full Cu41Sn11 solder joint (Cu/Cu41Sn11/Cu) during isothermal aging at 420°C. It was motivated by potential applications of Cu-Sn intermetallic compounds (IMC) solder joint in third-generation wide bandgap semiconductor devices. Experimental results revealed that the Cu41Sn11 phase was unstable under high-temperature conditions, the full Cu41Sn11 joint transformed into the full α(Cu) joint (Cu/α(Cu)/Cu) joint at 150 h during thermal aging. The formed α(Cu) phase was a Cu solid solution with inhomogeneous Sn atomic concentration, and its crystal structure and orientation were consistent with the original Cu plate. The conversion of the Cu41Sn11 to α(Cu) was accompanied by the formation of voids due to the volume shrinkage effect, predominantly near the middle of the solder joint interface. The α(Cu) solder joint presented a decrease in strength but an increase in strain rate sensitivity index compared to the Cu41Sn11 solder joint. Furthermore, the strain rate sensitivity index of α(Cu) and Cu41Sn11 is lower than that of ordinary Sn solders. After the shear test, the fractures that occurred in Cu41Sn11 grains were brittle, while the fractures in α(Cu) grains were ductile.

Purpose This study aims to analyse the changes in the microstructure and grain orientation of the full Cu3Sn solder joint (Cu/Cu3Sn/Cu) during isothermal aging at 420°C. Design/methodology/approach The Cu3Sn solder joint was fabricated through soldering Cu/Sn/Cu structure and then aged at 420°C. The microstructure evolution and grain orientation were studied by observing the cross-section and top-view surfaces of solder joints. Findings Original Cu3Sn solder joint initially transformed into the full Cu41Sn11solder joint (Cu/Cu41Sn11/Cu) at 10 h and finally into the full α(Cu) solder joint (Cu/α(Cu)/Cu) at 150 h during aging. Micro-voids formed in the center of the solder joint interface during the conversion of Cu41Sn11to α(Cu), resulting in lower reliability of the solder joint. Cu3Sn and Cu41Sn11 grains presented a column-like shape, while α(Cu) presented an irregular shape. The average grain sizes of interfacial phases first increased and then decreased during aging. Original Cu3Sn solder joint exhibited two main textures: [100]//TD and [203]//TD. For Cu41Sn11, the preferred orientation of [111]//TD was found in the early nucleation stage, while the orientation of the formed full Cu41Sn11 solder joint was dispersed. Furthermore, α(Cu) grains exhibited {100}<100> preferred orientation. Originality/value Few researchers focused on the process of microstructure and grain orientation changes during high-temperature (> 300°C) aging of Cu3Sn solder joint. To bridge the research gap, a high-temperature aging experiment was conducted on Cu3Sn solder joints.