Study On Preparation And Precipitation Phase Of Silicon Brass

Conventional leaded brasses are widely used in the pipe valves, machinery parts and other fields due to their superior workability in extrusion and drawing, together with their superior machinability. Pb was easy to precipitate, which is harm to human.Considering of its value, finding an alternative element is necessary. In this study, Si was choosed, together with several modified elements such as Ni, Sn, P and La. We made Si brass by smelting, hot rolling and cold rolling.The main contents and conclusions were as follows:Through the previous studies,we found that the second phase Si brass will precipitate, and it is mainly composed of Si, Ni and P. Its free cutting mechanism is as follows:Precipitates are dispersed in the substrate,which produced stress concentration,and make the chip easy to fracture. the concentration of solute in silicon brass will be smaller due to the precipitation.And the change of the concentration of solute in alloy may be expressed by the change of the conductivity.This paper employs resistance method to analyze the law of precipitation. Considering the dislocation in the as-cast brass is small. It is adversed for the second phase to nucleate and growth, So we set up a group of rolling state alloy which contained the same composition. Besides, the atom of solute diffuses slow at room temperature. It is difficult for the second phase to precipitate, so age treatment is taken for the alloy. giving aging treatment to casting and rolling states silicon brass respectively. We discussed the microstructure and mechanical roperties of Si brass under aging treatment. The conclusions are as follows:(1)By scanning electron microscopy(SEM), we find that the precipitation of the as-cast Si brass would increase With the extension of aging time. However, the precipitation was very few under each aging time. For rolling state Si brass,Organization rules along the rolling direction was arranged,αphase spheroidizing gradually, By EDS, we find In both the as-cast alloy and rolling state alloy, The second phase was contained of Si, Ni and P. And Si, Ni,P became more with the extension of aging time.(2)The different nickel content Si brass aged at 450℃ for 2h after soliding solution at 800℃ for 3h, precipitates distribute at the grain boundary of the as-cast alloy. It contained the precipitation wasαphase by EDS. With the Increament of Ni,there was more α phase distribute at the grain boundary, tensile strength of the alloyreduced gradually, and elongation risied gradually. For rolling Si brass, the tensile strength of alloy was highest when the contentment of Ni is 0.5%, and it was lowest when the contentment of Ni is 0.2%. The elongation was highest when the contentment of Ni is 0.2%, and it was lowest when the contentment of Ni is 0.5%.(3)The as-cast silicon brass with 0.5%Ni aged at 450℃ for 1h, 2h, 4h and 8h respectively, precipitates distribute at the grain boundary of the as-cast alloy.It contained the precipitation is α phase by EDS. With the extension of aging time, there was more αphase distribute at the grain boundary, Tensile strength rised first then falled, the peak was at 2h, it was 455MPa;and elongation falles firest then rised,it was lowest at 2h, for 26.5%.(4)The different nickel content Si brass aged at both 400℃,450℃and 550℃ for different time after soliding solution at 800℃ for 3h, under the same aging time,Tensile strength was highest at 450, and lowest at 400℃; elongation was highest at400℃, and lowest at 450℃; And no matter in which temperature, tensile strength of the alloy are diminishing with the increasement of aging time, The elongation rised with the increasement of aging time. In addition, the conductivity of the alloy was rised slowly with the extention of aging time.(5)In as-cast, with the extension of aging time, the electrical conductivity of alloy increased, but it was few.In rolling state,the conductivity of the alloy rised with the extension of aging time,Althoughe the amplitude is larger than the as-cast, it still small.For rolling state, during the aging process, reply and recrystallization happened in the alloy, it caused the density of defect reduced and the amount of grain boundary increased. These woule all affect its conductivity. When the change of electrical conductivity was small, It was difficult to analysis the relationship between the conductivity and the exudate,therefore, it was difficult to implement in the actual operation to analysis the rule of second phase precipitates in Si brass by using the resistance method.