Based on mass conservation in a typical micro-solidification volume element combining with previous work,a semianalytical model of microsegregation was established for binary alloys with dendritic solidification. The effects of back-diffusion and coarsening on microsegregation are both considered in the semi-analytical model,and the coarsening of arm spacing is directly calculated to make the semi-analytical model more precise. The semi-analytical model will be simplified to the BF model or the Mortensen mo...