The effects of Pr on the microstructure of as cast

solid solution and aging Al-5Cu alloy

as well as aging state on micro hardness and mechanical properties at room temperature and high temperature were investigated by OM

SEM and TEM

and the existing forms and mechanism of Pr were analyzed. The results show that Pr can refine effectively the α-Al dendrite in Al-5Cu alloy

and the dendrite size is decreased firstly and then increased with the increase of Pr content

and the minimum value can be observed with the Pr content of 0. 3%.The suitable heat treatment of Pr modified Al-5Cu alloy is 540 ℃ × 8 h solid solution + 165 ℃ × 10 h ageing treatment. When the aging temperature is 165 ℃ and 185 ℃ and 250 ℃

the average length of the θ’ phase in Al-5Cu alloy with 0. 3% Pr modification is reduced by 23. 2%

25. 6% and 31. 1%

respectively

compared with unmodified Al-5Cu alloy

and the number of precipitates is significantly more than the alloy without Pr modification. With the increase of Pr content

the tensile strength and elongation are increased at first and then decreased

and the maximum value is obtained when the content of Pr is 0. 3%. Tensile strength and elongation at room temperature and high temperature of the Al-5Cu alloy with 0. 3% Pr modification are higher than unmodified Al-5Cu alloy

and the main mechanism is characterized by fine grain strengthening and second phase strengthening.