Microstructural evolutions and mechanical characteristics of roll-bonding Mg/Al clad plate regulated by cold spraying micron particle interlayer

Abstract

A new process of “cold spraying interlayer + roll-bonding” (CSIR) was put forward for the preparation of Mg/Al clad plates. First, the micron Ni and Al powders (including some Zn particles) were cold sprayed to form an ultrathin coating on Al or Mg substrate slabs. Then roll-bonding was performed at 400 °C. The influence of cold sprayed coating on slab surfaces, interfacial microstructures, texture evolutions, mechanical properties and the related mechanism were systematically investigated. The results show that the average shear strength of the as-rolled Mg/Al clad plate assisted by cold spraying Al and Ni micron powders interlayer on the substrate slabs was nearly twice (35.58 MPa) than that of conventional rolling under the same conditions (single pass, reduction ratio was 35%). For as-rolled Mg/Al clad plates, almost no reaction diffusion layers are generated, and the mechanical interlocking between cold sprayed coatings and substrate slabs is the main mechanism for improving the shear strength. The interface between the Al coating and the Ni coating is weakest of the as-rolled Mg/Al clad plates. As the reduction rate increases from 27.5% to 47.5%, the function of the mechanical interlocking of cold sprayed coatings will first increase and then weaken. After annealing at 400 °C for 1 h, the interface between the Al coating and the Mg substrate slab will form thick mixed brittle intermetallic compounds, including Al3Mg2, Mg17Al12, MgZn2 and AlMg4Zn11, and cause local gaps, holes, and cracks around the Zn-rich Ni coating. The fracture path after annealing starts from the vicinity of the defective Ni particles, and eventually enlarges along the mixed intermetallic compounds layer between the Al coating and the Mg substrate slab. The research indicates that the CSIR process has great potential in cooperating the metallurgical bonding with the mechanical interlocking of clad plates.