Carbon fiber-reinforced plastic (CFRP), which is a light and composite material, has a higher specific strength and stiffness than metal materials. However, owing to its low elongation, it is vulnerable to local impacts such as collision. Therefore, hybrid composite materials that can overcome the disadvantages of homogeneous materials by bonding CFRP and metal materials are increasingly popular. In this study, a physical surface treatment sandblast process was applied on a high tensile steel plate (CR980) manufactured by cold rolling to form another surface condition, and the bonding strength with CFRP was measured. In addition, spring-back due to the manufacturing process of the CFRP and CR980 hybrid composite material bonded with different surface roughness was observed. The bonding strength and the spring-back angle of the CFRP/CR980 hybrid composite material tended to increase with the increase in the surface roughness.

In this paper, aluminium-based (Al6061) composites with 1, 3, 5, 7, and 10 vol % of multi-walled carbon nanotubes (MWCNTs) are investigated. The composites are fabricated by high-energy ball milling, cold-compacting at room temperature under compacting pressures of 400–1600 MPa, and sintering at 620 °C in an argon gas atmosphere. Thereafter, the hardness and microstructure of MWCNTs/Al6061 composites are examined. Further, to improve the relative density and hardness level of the complex material, open-die forging is performed after cold-compacting under 1 GPa pressure at room temperature and sintering at 620 °C. The open-die forging parameters include 1, 3, 5, 7, and 10 vol % MWCNTs/Al6061, and Al6061. The experimental results show that the mechanical properties of the composites are significantly superior to that of the Al6061 alloy after undergoing cold-compacting, sintering, and open-die forging.