Abstract: In this paper, strength rate of strength increase, range of quasi-solid and failure strain of Al-Cu alloys in quasi-solid during solidification are investigated with special apparatus-The relationship between the mechanical properties of Al-Cu alloys in the quasi-solid and solidification process is analyzed. The influence of Ti, salt-refiner and mischmetal on the mechanical properties is also studied. Results obtained show that quasi-solid us divides the solid-liquid coexisting zone of hypoeutectic Al-Cu alloys into range of quasi-liquid and range of quasi-solid. With less than 4%Cu, the range of quasi-solid can be subdivided into range of hot brittleness and range of low strength plasticity. The mechanical properties in the range of low strength plasticity are obviously lower than those in the range of hot brittleness, but a little liquid still exists in interdendrite boundaries. With more than 4%Cu, the range of quasi-solid is equivalent to the range of hot brittleness. Strain rates .and the trace additions are able to change the mechanical properties of A1-Cu alloys in the quasi-solid.