The brazing ribbons and as-cast solder of Al-Cu with the same compositions were prepared by means of rapid solidification and ordinary casting method,respectively.These two kinds of solders were used to pure braze aluminum with vacuum brazing at 590,600,610,and 620 ℃ during the time periods of temperature holding as 5,10,15,and 20 min.The melting points,microstructures,and diffusibility of Cu were studied with DTA,SEM,X-ray,and EDS.The results showed that the elements of the rapid solidified solder ribbons have homogeneous structure and very small crystal grain size and,as to the ordinary Al-Cu solders,there was crystal segregation and pine-tree crystal.Its melting point was lower than that of ordinary Al-Cu solder by 3.0 ℃,and crystallizing range is narrower than that of ordinary Al-Cu solder by 1.2 ℃.When the soldering temperature and soldering heat-retaining period was identical,the Cu diffusibility of the rapid solidified solder was remarkably higher than that of the ordinary solder.Discrimination of diffusivity reduced with the increase of soldering temperature and prolonged heat-retaining period.