PSI - Issue 13

Saeed Mousa et al. / Procedia Structural Integrity 13 (2018) 686–693 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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1. Introduction

Roll bonding can be used to join various combinations of metal sheets, such as Al/Al sheets, Cu/Al layers, and stainless steel/Al sheets for automotive, electrical, and kitchen utensil applications. Typical roll bonding includes a sequence of chemical or mechanical surface treatments of the metal sheets, stacking of the sheets, and rolling (Madaah-Hosseini at el., 2002). Rolling can be conducted at room temperature or at elevated temperatures. Threshold reduction, the minimum value of single-pass reduction for successful bonding, can be reduced by increasing the rolling temperature (Abbasi at el.,2010). To achieve successful bonding, it is essential to clean the bonding surfaces. Cold roll bonding often requires sanding prior to rolling because chemical degreasing is not sufficient to prepare the surfaces. Using sandpapers will help to remove surface layers composed of contaminated layers and oxide layers. More importantly, it forms a hardened cover layer on the surface (Kim, Su-Hyeon, et al. 2012) and increases surface roughness. Sanding increases the hardness and roughness because the roughened surface, exposed to air, becomes oxidized and contaminated quickly after sanding. In warm rolling, sanding is a prerequisite for good bonding properties (Nezhad at el., 2009),(Mousa and Kim, 2015), (Mousa and Kim, 2017). In the present work, the Al1100/brass/Al1100 sandwich composite was fabricated by warm roll bonding (WRB). The effects of the non-damaged zones after sanding on direct adhesion strength were analyzed experimentally and theoretically. The maximum undamaged defect size ( d max ) suggested by Sallam et al. (2014), Abou El Mal et al (2015) will be adopted in the present work to examine the quality of the contact surface. The main objective of the present work is to generalize the d max concept to predict the maximum size of circular imperfection in Al-brass interface beyond which its peeling strength will be decreased. A commercially pure aluminum (Al1100) strip and brass sheets were used to make the sandwich composite. The strips were cut into dimensions of 60 mm × 20 mm × 0.5 mm. Also, the brass sheets were cut into dimensions of 60 mm × 20 mm × 0.5 mm. The specification of Al1100 strips and brass sheets are summarized in table 1. The preheating of Al1100 samples was accomplished using a heat plate (Cimarek) at different temperatures for 15 min. Then, each sample was assembled by inserting the brass sheet between the two Al1100 strips. The samples were joined by a rolling mill (Durston-DRM 130) with a roll diameter of 65 mm, and at rolling speed of 45 rpm. The reduction ratio that used in the experiments was about 60%. In order to produce a satisfactory bond in WRB, it is important to remove the contaminated layers on the surfaces of the strips. The sample surfaces were first degreased with ethanol, followed by sanding of the surface. Sandpapers with average grit sizes of 80 and 50 were used to investigate the effect of surface roughness on the bond strength. The bonding took place immediately after degreasing and sanding to avoid surface oxidation. It was noticed during the sanding that there are some areas on aluminum surface that has some imperfections. The adhesion between the core and the metal sheets was investigated by T (180°) peel test according to the DIN53282. The peel test was performed using a universal testing machine (TestResources Inc.) with a crosshead speed of 20 mm/min. The average peel strength can be calculated as average load (N)/bond width (mm). Table 1: Specification of Al1100 strip and brass sheet. Symbol Value Property E,  ,  y ,  u 75, 0.33, 169, 186 Young's modulus (GPa), Poisson's Ratio, Yield stress (MPa), Tensile strength (MPa), respectively, for aluminum 99, 0.29, 124, 338 Young's modulus (GPa), Poisson's Ratio, Yield stress (MPa), Tensile strength (MPa), respectively, for brass 99.61 Al, 0.11 Si, 0.55 Fe, 0.11 Cu, 0.07 others Chemical composition of aluminum (wt.%) 91 Cu, .0.5 Pb, 0.05 Fe, Zn balance Chemical composition of brass (wt.%) 2. Experimental procedure