In this paper, an ultra-thin Cu/Al composite sheet with a thickness of 0.08 mm was obtained via the cold-rolling composite method using a four-high micro-rolling mill in the laboratory. The rolling reduction of a single pass was 65%. After the annealing of the ultra-thin Cu/Al composite sheets at temperatures ranging from 350 °C to 500 °C, the interface bonding mode of the Cu/Al composite sheets changed from mechanical bonding to metallurgical bonding, and the bonding strength was significantly improved. The microhardness value at the bonding interface of the ultra-thin Cu/Al composite sheets increases with the increase in annealing temperature. When the annealing temperature is 500 °C, the maximum microhardness value at the bonding interface reached 2.0 GPa. With the increase in annealing temperature, the tensile strength and elongation of the ultra-thin Cu/Al composite sheets decreases significantly. The peel strength of the extremely thin Cu/Al composite sheets increases at first and then decreases with the increase in annealing temperature, and reached the maximum value at an annealing temperature of 400 °C. When the annealing temperature was 400 °C, the tensile and peel properties of the ultra-thin Cu/Al composite sheet reached the best state.

The microstructure and micro-hardness of tungsten carbide/high strength steel (WC/HSS) composites with different particle sizes were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), ultra-high temperature laser confocal microscopy (UTLCM) and micro-hardness testing. The composites were prepared by cold pressing and vacuum sintering. The results show that WC density tends to increase as the average grain size of WC decreases and the micro-hardness of WC increases with the decrease of WC particle size. The micro-hardness of WC near the bonding interface is higher than that in other regions. When the particle size of WC powder particles is 200 nm, a transition layer with a certain width is formed at the interface between WC and HSS, and the combination between the two materials is metallurgical. The iron element in the HSS matrix diffuses into the WC structure in contact with it, resulting in a fusion layer of a certain width, and the composite interface is relatively well bonded. When the average particle size of WC powder is 200 nm, W, Fe and Co elements significantly diffuse in the transition zone at the interface. With the increase of WC particle size, the trend of element diffusion decreases.

In this study, WC-Co-TiC/304 stainless steel composites were successfully prepared by compression at room temperature and vacuum sintering in a special mold. Through analysis and comparison of the microstructure, density, and particle size of WC-Co-TiC/304 stainless steel composite, the effects of different WC contents on the structure and properties of WC-Co-TiC were studied. The results show that among different WC contents when the WC content is 60%, the distribution of each structure is relatively uniform and fine, and the agglomeration of each structure is not obvious. The bonding effect of WC-Co-TiC cemented carbide and 304 stainless steel composite interface is the best. With the increase of WC content, the side defects of WC-Co-TiC cemented carbide increase gradually. When WC content is 60%, the best ratio is 1:1 of Co/TiC, as the density is 94.45%, the particle size of 0.2–0.3 μm is 38.9%, and the highest hardness of WC-Co-TiC cemented carbide side is 1370 HV_0.1, but it is better when the ratio of Co/TiC is 3:2 at the composite interface, as the hardness value is 852 HV_0.1 and the diffusion of Cr element is more uniform, while other elements have little difference.

In this paper, the influence of bismuth content and heating rate on the morphology of MnS inclusions in bismuth-containing free-cutting steel during heating was investigated through in situ observation experiments and 3D electrolytic corrosion experiments. By observing the microscopic morphology of inclusions in the original sample, it was found that MnS inclusions in the sample were rod-shaped, spherical, irregular, small in size, and mostly clustered at the grain boundary in the form of chains and divergences. With the addition of bismuth, MnS inclusions of a larger size appear in the steel, and the inclusions distributed at grain boundaries are also reduced. When bismuth (0.010~0.020%) is added to the steel, MnS is mainly spherical and uniformly dispersed in the steel matrix. If the bismuth content is too high, the inclusions aggregate. Through in situ observations of the inclusions in the sample, it was found that the addition of bismuth in the heating process delays the appearance of ferrite grain boundaries and contributes to the spheroidization of MnS inclusions. Mn and S elements can fully diffuse slowly in the matrix with a heating rate below 1 °C/s and a long holding time (300 s), which provides the possibility for the spheroidization of MnS inclusions.