OBRABOTKAMETALLOV technology Vol. 25 No. 3 2023 At a reduction ratio of 75 %, the reverse pattern is observed: the central layer of the composite is characterized by large values of the effective strain ei. This phenomenon is most likely caused by the small thickness of the sheet (2.2 mm) at this reduction ratio, which leads to a more intense propagation of the deformation into the depth of the composite. In general, the maximum scatter of the effective strain (max) (min) (max) 100% i i i e e e − is 12 %, which was observed at a thickness reduction ratio of 75 %. Therefore, it is possible to make an assumption about the uniformity of the strain distribution in the cross section of the composite “AMg3/D16/AMg3” in the first approximation for analytical calculations of the manufacturing technology. To study the conditions of the bond formation between layers from different materials, the degree of surface extend 1 0 1 A A Y A − = was calculated for different rolling options, where A0 and A1 are the initial and final surface areas [14, 21]. To determine the beginning of the bond formation in the deformation zone, the boundary criterion Y´ was set, which means the contact surface extend, at which cracks appear in the oxide layer. According to the literature sources [6, 14, 16, 17, 18, 22] devoted to the production of aluminum composites by rolling, Y´ criterion can vary from 0.3 to 0.4 for commercially pure aluminum, which is equivalent to an approximate rolling reduction ratio ε of 30–40 %. In our case, Y´ criterion was taken equal to 0.3, considering the lower ductility of the studied alloys compared to commercially pure aluminum. Fig. 5 shows the dependence of the extend of the contact surface Y at the interlayer boundary on the relative length of the deformation zone, where “0” is the entrance to the deformation zone, “1” is the exit from the deformation zone. Additionally, the same figure shows normal pressure. Analysis of the surface extend values Y at the exit from the deformation zone in fig. 5 reveals that these values practically coincide with the reduction ε values. This suggests that the influence of the lateral broadening of sheets on the contact surface extend Y is negligible and can be neglected for analytical calculations under these conditions. Fig. 5a presents the case of rolling of the three-layer pack “AMg3/D16/AMg3” with a rate of reduction equal to 30 %. As can be seen, the contact surface extend Y crosses the threshold exposure Y´ at a relative length of 0.8 of the deformation zone, which corresponds to the onset of cracking of the oxide layer and the possibility of contact between pure metals. However, at a relative length (0.8–1) of the deformation zone, normal pressures are intensively reduced from 250 to 0 MPa. Thus, the maximum relative pressure 16 D p σ is 1.5, which is not enough to create contact between the materials. Under real conditions of rolling with a reduction of 30 %, bonding between aluminum alloys does not occur, which is consistent with the computer simulation data of the presented case. Fig. 5b shows a dependence of the contact surface extend and normal pressure on the relative length of the deformation zone during rolling with a reduction of 45 %. In this variant, the achievement of the threshold value of the contact surface exposure Y´ occurs at a relative length of the deformation zone equal to 0.42. After reaching the threshold value, the contact surface continued to extend and Y reached a value of 0.45. At the relative length of the deformation zone (0.42–1), corresponding to rolling with cracks in the oxide layer, the pressure continued to increase from 320 MPa to a maximum value of 394 MPa. The relative pressures 16 D p σ in the area of the deformation zone range from 1.6 to 1.97. Since the primary bonding of materials is formed during rolling with a reduction of 45 % under laboratory conditions, it can be assumed that relative pressures from 1.6 to 1.97 are sufficient to extrude pure metals between cracks in the oxide layer and bring it to the distance of action of interatomic forces. To confirm the results of the computer simulation, the data of the microstructural study of laminated composite “AMg3/D16/AMg3” after rolling with a reduction of 45 % are shown in fig. 6. Fig. 6a presents the cross section of the composite in the area of material bonding. The bonding boundary is a visible line, with no signs of cracking or fracture of structural elements. After rolling, the laminated composite was
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