In this work, we analyze the anharmonic phonon scattering time to project the acoustic loss limits in thin-film aluminum scandium nitride (Al 1-x Sc x N) micromechanical resonators. Although electromechanical coupling coefficients have been improved significantly with Sc alloying, making Al 1-x Sc x N a promising material for wideband acoustic filters, lower quality factor (Q) have been observed when increasing Sc content in Al 1-x Sc x N. This has often been attributed to poor crystallinity and surface roughness of the film. To investigate the intrinsic limiting factors of Q in Al 1-x Sc x N resonators, we summarize the figure of merits from the experimental works of Al 1-x Sc x N resonators from multiple research and industry groups in the past decades. We classify the major phonon scattering mechanisms present in Al 1-x Sc x N lattice and their theoretical expressions. The results suggest that while both AlN and Al 1-x Sc x N phonon lifetimes can be limited by grain boundary scattering, which depends on the crystal microstructure, as well as the film thickness, Al 0.7 Sc 0.3 N suffers from a decrease of phonon lifetime by up to four orders of magnitude due to alloy scattering, conceivably responsible for the lower Q compared to AlN acoustic resonators.