Roll Welding Experiments: The Roll Welding Process

The roll welding experiments were carried out using a technical lab rolling machine with 170 mm roll diameter, 36 rpm of rotational speed and a power capacity of 35hp is used. To protect the rolling machine from damage caused by current ‘‘leakage’’, ceramic sleeves were applied on the roll shafts for electrical insulation. After surface provision, the handling of strips was performed intently to eschew renewed contamination. The gap between surface provision and rolling process was kept to less than two minutes to avoid the formation of a thick and continuous oxide layer on the bond surfaces of the strips. Then, according to Figure 1(a), one end side of stacked strips were connected to a welding machine with capacity of 400 amperes. The steps of the manufacture process of the Al/ Al2O3 composite have been summarized in Table 3.

For the first EARB cycle, the Al/ Al2O3/Al sample were roll-bonded at 50% reduction (effective strain equal to 0.8) at the ambient temperature without any lubrication to obtain 1mm strip thickness (Fig. 1(a)). Electricity current intensity and thickness reduction are two key factors in EARB process for an acceptable bonding of composite layers and avoiding exfoliating. Increasing the amperage cause to enhance the bonding strength among the composite layers and by increasing thickness

According to Figure 2, at constant current levels, the strength are considerably increases by the first cycle up to the 6th cycle. For example, for samples ARB produced (without electricity current), the tensile strength increases from 270 MPa for the annealed sample to 484 MPa after the second cycle, registering 79.26% improve. Always, the increment in UTS in ARB process is rather small, except in the case of initial cycles. This behavior can be explained based on two mechanisms: (Ι) strain hardening (dislocation strengthening) and (ΙΙ) production of ultra-fine grains (grain refinement) [9,