The effects of quenching conditions on intergranular corrosion behavior and mechanical properties of Al-Mg-Si-Cu alloys with high Cu were investigated. Results indicate that quenching conditions plays a pivotal role in boundary precipitates at fibrous fine regions. Under water-quenching conditions, the grain boundary precipitates are mainly discontinuous Q' phases. Interestingly, the precipitates are dense and continuously distributed at low-angle/sub-grain boundaries under air-quenching conditions. It intensifies the boundary corrosion tendency at misorientation <10°, resulting in poor corrosion resistance for air-quenching alloys. Therefore, Al-Mg-Si-Cu profiles with high Cu prepared by water quenching after extrusion can obtain superior mechanical properties and corrosion resistance.