Sizes effect on the tensile behaviors of H65-IF-H65 laminated metal composites

The H65/IF/H65 laminated metal composites (LMCs) not only have the good electrical conductivity, thermal conductivity and corrosion resistance of the outer H65 layer, but also combine the excellent strength, plasticity and formability of IF layer in the middle. In view of the great potential application of H65/IF/H65 LMCs in microelectronic components, which will inevitably face the extrinsic sizes effect brought by the processes such as microstretching or microforming, the influence and mechanism of sample width on the mechanical properties of H65/IF/H65 LMCs with optimised layer thicknesses and their ratios were studied.

The H65/IF/H65 LMCs were prepared by commercial H65, IF, H65 sheets by rolling combined with annealing. Tensile specimens with gauge widths of 1, 2, 3, 4, 5, 9 mm and length of 25 mm were prepared by electric spark cutting along the rolling direction. The routine tensile tests were subjected to an Instron 3369 electronic universal test machine equipped with a non-contact video extensometer AVE 2. The strain distribution during stretching was analyzed by the digital image correlation DIC technique. The grain size and orientation distributions of the lateral H65 layers and the middle IF one were observed by FEI Nova Nano SEM 450 scanning microscope with EBSD, HKL/Channel 5 system. The element distribution, fracture morphology and surface roughness of H65/IF/H65 LMCs during stretching were observed by a phenom XL SEM equipped with an EDS device and 3D roughness software. The initiation and propagation of cracks were observed using an in-situ stretching table with a 1kN load.

(1)The thickness of the H65/IF/H65 LMCs was about 120 μm, in which the average thicknesses of the middle IF layer and the unilateral H65 one were about 100 μm and 10 μm. The average grain sizes of the IF and H65 layers were 20.9 μm and 9.6 μm, respectively. There was no elements diffusion at the H65/IF interface which means a mechanical bonding.(2)The total elongation, yield strength and tensile strength of the H65/IF/H65 LMCs sample with a 9 mm gauge width were 37.5%, 218.9 MPa and 302.0 MPa, respectively. The total elongation showed a monotonically decreasing trend with a decreasing specimen width as the above values of the sample with a 1 mm gauge width were 20.2%, 209.8 MPa and 287.5 MPa, respectively. The ability of the H65/IF/H65 LMCs to resist plastic instability decreased with the decreasing gauge width, and the plasticity was more susceptible to the influence of gauge width than the strength. (3)With the reduction of the gauge width from 9 mm to 1 mm, the deformation inhomogeneity in the gauge area of the H65/IF/H65 LMCs became more apparent, and the surface roughness Ra decreased form 1.84 μm to 1.45 μm when the sample was stretched to the necking point. The shear stress interaction was stronger when the gauge width was 9 mm. The cracks initiated from the inside of the specimen along the shear band and formed a step-like propagation under the influence of several pairs of staggered shear bands. When the gauge width was decreased to 1 mm, the shear stress interaction was suppressed, and the several pairs of staggered shear bands structures were merged into a single shear one. The cracks initiated on one side of this shear band and rapidly propagated along it without a step-like deflection. (4)The H65 layer was stripped and shed in the area near the fracture. With the reduction of the gauge width from 9 mm to 1 mm, the width of the dimple band, as well as the number and size of dimples within it also decreased significantly, and a relatively sharp tip was formed in a localized area of the fracture.Conclusions: There is a significant sizes effect on the tensile behaviors of H65/IF/H65 LMCs with the reduction of the gauge width from 9 mm to 1 mm. This effect mainly originates from the fact that the shear stress interaction was suppressed with the reduction of the gauge width. When the gauge width was small, the crack was more prone to propagate rapidly along the single shear band and resulted in a decreased ductility.