Pure copper was subjected to high-pressure surface rolling (HPSR) to obtain a surface gradient layer. Effects of HPSR parameters on the surface microstructure and microhardness of Cu were investigated by using optical microscopy, transmission electronic microscopy, X-ray diffraction, and the microhardness test. The HPSR surface layer has a gradient microstructure consisting of increasingly refined grains with decreasing depth from the treated surface (DFS). The thicknesses of the refined surface layer can be up to ~1.8 mm, and the grain size of the topmost surface is down to ~88 nm, depending on the HPSR parameters including pressure, time, and temperature. Microhardness of HPSR samples increases with decreasing DFS, with a maximum of ~2.4 times that of the undeformed matrix. The present results indicated that HPSR could be an effective method for the production of a mm-thick surface layer on Cu with gradient microstructure and property.

The liquid thermal history effect on liquid supercooling behavior has been found in various metals and alloys; typically the degree of liquid supercooling (ΔT⁻) increases with the increase of liquid overheating (ΔT⁺) up to several to tens of degrees above the equilibrium melting point (T₀). Here we report quantitative experimental measurements on the ΔT⁻-ΔT⁺ relationship of Al small particles encapsulated in Al₂O₃ shells by using a differential scanning calorimeter. We find a remarkable dependence of ΔT⁻ on ΔT⁺ of Al small particles, extending to at least 340 °C above T₀ of Al (~1.36T₀), which indicates the existence of temperature-dependent crystallization centers in liquid Al up to very high liquid overheating levels. Our results demonstrate quantitatively the significant effect of liquid thermal history on the supercooling behavior of Al and its alloys, and raise new considerations about the dependence of ΔT⁻ on ΔT⁺ at very high ΔT⁺ levels.

To meet the stringent demands of advanced applications, such as high-frequency communications and next-generation energy storage, the production of high-performance electrodeposited copper foils is needed. The mechanical properties of Cu foils are highly dependent on various electrodeposition parameters, leading to challenges in the electrodeposition process optimization. This study presents a systematic investigation into the individual and synergistic roles of titanium cathode surface grinding processing/roughness and current density in determining the microstructure and properties of electrodeposited copper foils. The results reveal that the surface roughness parameter RS _m is the critical cathode parameter that correlates strongly with the enhanced tensile strength of Cu foils. Furthermore, an optimal current density exists for a given cathode roughness, maximizing foil performance through microstructural refinement. By synergistically optimizing the Ti cathode with low RS _m and the proper current density, we successfully fabricate copper foil with a tensile strength of 615 MPa and a low-profile surface with roughness of R _z = 0.45 μm. Microstructure investigations showed that the cathode roughness and current density can affect the microstructure characteristics of Cu foils, including the grain size, twin thickness, texture, and GND distribution, providing a microstructure basis for understanding the electrodeposition parameter-tensile strength relation. This work provides an electrodeposition parameter basis for optimizing the properties of electrodeposited Cu foils.