Effect of Al2O3 Inclusions or Mold Flux Particles on Their Surrounding Microstructures of Sliver Defects on the Surface of Automobile Exposed Panel

The Al2O3 inclusions and mold flux particles are the initial causes of the sliver defects on the surface of automobile exposed panels. During the rolling process, the smashed Al2O3 inclusions or mold flux particles will hinder the growth of recrystallized grains. Compared with mold flux particles, the smashed Al2O3 inclusions have a smaller size, a denser distribution, and a larger number density, so the smashed Al2O3 inclusions have a stronger ability to hinder grain boundary migration. Therefore, the average grain size is small in the following sequence: Al2O3 defect zone with Al2O3 inclusions (Al2O3 DZ with Al2O3), mold flux defect zone with mold flux particles (MFDZ with MFP), mold flux defect zone without mold flux particles (MFDZ without MFP), Al2O3 defect zone without Al2O3 inclusions (Al2O3 DZ without Al2O3), and non-defect zone (NDZ). The influence of particles on the grain orientation of the defect zones results in the microtexture of Al2O3 DZ without Al2O3 is {111}, which is close to the {111} microtextures of NDZ and MFDZ without MFP, while the {001} microtexture on Al2O3 DZ with Al2O3 and the {313} microtexture on MFDZ with MFP are quite different from that of NDZ. Due to differences in the inclusions, orientation, and microtexture of the defect zones and NDZ, dark-gray or bright white sliver defects on the surface of the automobile exposed panel are eventually formed.