2023 Volume 64 Issue 2 Pages 366-372
In this study, the effects of the roll load and superheating on the appearance of surface defects in Al–Mg and Al–Si alloy strips cast using a high-speed twin-roll caster were investigated. The band zone that existed in the center of the thickness direction was investigated. The alloy compositions were Al–4.8%Mg and Al–Si with Si contents of 1, 2, 3 and 11%. The diameter and width of the copper roll in the twin-roll caster were 300 and 50 mm, respectively. The superheating temperature of the molten metal was 5 and 50°C, and the roll load was varied from 2 to 88 N/mm. A roll speed of 30 m/min was utilized. The existence of surface cracks was investigated by penetrant inspection and bending test. The amount of surface cracking in the Al–Mg alloy was affected by the roll load, and the number of surface cracks decreased with decreasing roll load. Surface cracks occurred more easily in the Al–4.8%Mg alloy than in the Al–Si alloys. The degree of cracking could not be reduced by cold-rolling. In the Al–Si alloys, the ripple marks were affected by the Si content, degree of superheating of the molten metal and the roll load. In the Al–3%Si alloy, ripple marks were produced, and worsened as the roll load and the superheating of the molten metal were increased. A specimen for observation of the microstructure near the roll bite was obtained by performing a roll-stop during casting, and observed using Weck’s reagent. A band zone was found to exist. The band zone in Al–Si consisted of globular crystals, and that in Al–Mg consisted of equiaxed dendrites and Mg-rich areas.
