Preparation, structure and properties of Mg/Al laminated metal composites fabricated by roll-bonding, a review

Laminated metal composites(LMCs) are a unique composite material and have great application prospects in automobiles, ships, aircraft,and other manufacturing industries. As lightweight materials, the Mg/Al LMCs are expected to combine the advantages of both Mg and Al alloys to broaden their application prospects. Roll-bonding is the most popular process for the fabrication of Mg/Al LMCs due to high production efficiency and good product quality stability. The roll-bonding process involves the deformation of the substrates and the formation of the interfacial diffusion layer. The latter will directly determine the interface bonding strength of Mg/Al LMCs. Bonding strength is very sensitive to the thickness of the reaction layer in the diffusion layer. When the thickness of the reaction layer exceeds 5 μm, the bonding strength decreases sharply. Therefore, controlling the thickness of the reaction layer is very important for the design of rolling parameters.The latest research also showed that the addition of intermediate layer metal and the construction of three-dimensional interfaces can further improve the interface bonding strength. How to apply these methods to roll-bonding is the focus of future research. Recently, a new rolling technique, corrugated roll/plat roll rolling+flat roll/flat roll rolling has been developed to fabricate Mg/Al LMCs. It can effectively promote the deformation of the hard layer and generate a wavy interface, resulting in the enhancement of the bonding quality and rolling quality.In the current review, the effects of rolling parameters and subsequent annealing on the interface structure of Mg/Al LMCs were elaborated in detail. The application of some special rolling techniques in the preparation of Mg/Al LMCs was also summarized. The latest research results on the relationship between interface structure and mechanical properties of Mg/Al LMCs were reviewed. Finally, further research directions in this field were proposed.

Effect of lamellar structural parameters on the bending fracture behavior of AA1100/AA7075 laminated metal composites

The lamellar structure has an important impact on the mechanical properties of dissimilar laminated metal composites(LMCs),including the thickness ratio of dissimilar metal constituent layers and the number of layers.AA1100 and AA7075 with thickness ratios of 1:4 and 3:4 were fabricated for multilayer AA1100/AA7075 LMCs by hot accumulative roll bonding(ARB)technology.The bending fracture characteristics of AA1100/AA7075 LMCs with different thickness ratios and numbers of constituent layers were investigated.The research results indicated that AA1100/AA7075 LMCs with a low thickness ratio exhibited better bending ductility and toughness than those with a high thickness ratio,which was attributed to the crack growth resistance caused by the thickness of the soft AA1100 layer.The toughening mechanism introduced by crack deflection or arresting contributed to the enhancement in the toughness of the LMCs compared with that of the single 7075 Al layer.The bonding interfaces of AA1100/AA7075 LMCs with different numbers of layers are continuous and straight due to the high ARB temperature.A decrease in bending toughness was observed as the number of layers increased.Unlike LMCs with a low number of layers,crack deflection or interface delamination is also considered a main toughening mechanism in dissimilar LMCs in addition to the thickness effect.

Shear banding-inducedslip enables unprecedented strength-ductility combination of laminated metallic composites

Shear bands in metallic materials have been reported to be catastrophic because they normally lead to non-uniform plastic deformation. Ductility of laminated metallic composites deteriorates with increasing processing strain, particularly for those having hexagonal-close-packed(hcp) constituents due to inadequate slip systems and consequently prominent shear banding. Here, we propose a design strategy that counterintuitively tolerates the bands with localized strains, i.e. the shear banded laminar(SBL) structure, which promotes <c+a> dislocation activation in hcp metals and renders unprecedented strengthductility combination in hcp-metal-based composites fabricated by accumulative roll bonding(ARB). The SBL structure is characterized with one soft hcp metal constrained by adjacent hard metal in which dislocations have been accumulated near the bimetal interfaces. High-energy X-ray diffraction astonishingly reveals that more than 90% of dislocations are non-basal in Ti layers of the SBL Ti/Nb composite processed by eight ARB cycles. Moreover, <c+a> dislocations occupy a high fraction of ~30%, promoting further <c+a>cross slip. The unique stress field tailored by both shear banding and heterophase interface-mediated deformation accommodation triggers important <c+a> slip. This SBL design is of significance for developing hcp-based laminates and other heterostructured materials with high performances.

Improving Ductility and Anisotropy by Dynamic Recrystallization in Ti/Mg Laminated Metal Composite

Ti/Mg laminated metal composites(LMCs)were processed by hot roll bonding and subsequent annealing at 200℃and300℃for 1 h,and the effect of dynamic recrystallization on the microstructure and anisotropy behavior was investigated in detail.The results revealed that,in both as-rolled and annealed Ti/Mg LMCs,the inhomogeneous distribution in the microstructure of Mg layers near the interface and near the center was related to the effect of friction between the roller and sheet surface and uncoordinated deformation between constituent layers.With increasing annealing temperature,Ti/Mg LMCs exhibited excellent elongation without sacrificing strength properties,which was mainly due to the improvement in bonding strength and the increasing strain gradient at the interface between soft and hard layers after annealing treatment.Besides,the increasing Schmid factors(SFs)of prismatic slip and pyramidal slip in Mg layers contributed to the improved plastic deformation ability of Ti/Mg LMCs.The experimental analysis indicated that the presence of Mg alloys resulted in the microstructure and mechanical properties of LMCs were different along various loading directions,and annealing treatment can effectively inhibit the anisotropic behavior of Ti/Mg LMCs resulting from the weakening of basal texture in the Mg layer.

A novel laminated metal composite with superior interfacial bonding composed of ultrahigh strength maraging steel and 316L stainless steel

A 5-layer laminated metal composite composed of ultrahigh-strength maraging steel and ductile 316L stainless steel was fabricated by hot pressing in vacuum and post-heat treatment.Microstructure characterization on hierarchical structure of the composite before and after heat treatment was made by optical microscopy,scanning electron microscopy and electron back-scattered diffraction technique,respectively.Meanwhile,the difference of mechanical performance on both sides of the interface was characterized by nano-hardness testing.Uniaxial tensile test showed that superior interfacial bonding was achieved due to the micro-‘bite’structure between the two steels without obvious defects or oxides at the interface and with coordinated deformation of the two components.Thus,a laminated metal composite consisting of two different constituents with extreme difference in strength can be well fabricated.

Interface Analysis and Hot Deformation Behaviour of a Novel Laminated Composite with High-Cr Cast Iron and Low Carbon Steel Prepared by Hot Compression Bonding

A hot compression bonding process was developed to prepare a novel laminated composite consisting of high-Cr cast iron （HCCI） as the inner layer and low carbon steel （LCS） as the outer layers on a Gleeble 3500 ther- momechanicat simulator at a temperature of 950 ℃ and a strain rate of 0. 001 s 1. Interfacial bond quality and hot deformation behaviour of the laminate were studied by mierostructural characterisation and mechanical tests. Experi- mental results show that the metallurgical bond between the constituent metals was achieved under the proposed bonding conditions without discernible defects and the formation of interlayer or intermetallic layer along the inter- face. The interfacial bond quality is excellent since no deterioration occurred around the interface which was deformed by Vickers indentation and compression test at room temperature with parallel loading to the interface. After well cladding by the LCS, the brittle HCCI can be severely deformed （about 57 % of reduction） at high temperature with crack-free. This significant improvement should be attributed to the decrease of crack sensitivity due to stress relief by soft claddings and enhanced flow property of the HCCI by simultaneous deformation with the LCS.