OBRABOTKAMETALLOV Vol. 25 No. 3 2023 technology Ta b l e 1 Surface topography parameters of AMg3 and D16 alloys after grinding with 40 and 120 grit bands Material/type of grinding Average roughness Ra, μm Total height of profile Rt, μm Average angle of the top of asperities The ratio of the height of asperity to the width of asperity base AMg3/40 grits 7.52 126.19 57° 0.33 AMg3/120 grits 5.66 116.19 49° 0.43 D16/40 grits 5.03 46.24 60° 0.29 D16/120 grits 5.13 55.15 40° 0.6 the lower the roughness parameters Ra and Rt are. Grinding by belts with different grits had an unequal effect on the materials under study. Changing the grain size of belts from 40 to 120 grits led to a decrease in the roughness parameters Ra and Rt and to a decrease in the average asperity top angle of the AMg3 alloy. At the same time, there was a slight increase in the roughness parameters Ra and Rt and a decrease in the average asperity top angle of the D16 alloy. The obtained average asperity top angles for all materials are in the range of 40–60°, and the ratio of the asperity height to the asperity base width H/W is in the range of 0.29–0.6. According to the theoretical model [18], the relative penetration depth hl/H should lie in the range of 0.56–0.64 by the time the plastic deformation begins to propagate in the bulk of the soft material, where hl is the depth of penetration of hard material asperities into the soft material. The reduced normal stress σ/k at the contact of materials should be in the range from -2.4 to -3.09, where k is the shear strain resistance of the soft material. Study of Plastic Deformation of Dissimilar Materials on a Microscale As indicated in the research methodology, the surface profiles of AMg3 and D16 materials were brought into contact, after which plastic deformation was initiated. Fig. 5 shows the initial moment of contact of the materials’ surfaces after belt grinding with 40 and 120 grits in a random central section of representative volumes. As can be seen, the actual pattern of contact between materials in this section does not repeat the idealized theoretical model in its pure form: periodically repeating asperities have different shapes and sizes; opposite the asperities of one material, both asperities and cavities of another material can be located. Accordingly, the stages described in 1.2, will occur nonsimultaneously over the entire contact area during the process of plastic deformation. To assess the stages of accumulative roll bonding of dissimilar materials, the effective strain intensity scale was adjusted with an upper threshold level of 120 MPa, which is equivalent to the yield strength of AMg3 alloy. When the nodal points of FE reached 120 MPa, the corresponding areas of the materials were highlighted in red, which meant the transition of the material to the plastic state. When the entire volume of both materials reached 120 MPa, the scale was reconfigured to the next upper level of 200 MPa, which corresponded to the maximum value of the strain resistance of the D16 alloy. The key stages of accumulative roll bonding of materials preliminary grinded by 40 grit belt are shown in fig. 6, and those preliminary grinded by 120 grit belt are shown in fig. 7. Fig. 5. Contact of surfaces of AMg3 and D16 alloys before plastic deformation in a random cross-section
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