Fine-grain tin-phosphor bronze alloy strip and a preparation method thereof

A preparation method of a fine-grain tin-phosphor bronze alloy strip, wherein, the preparation method comprises:

• subjecting a pretreated tin-phosphor bronze alloy strip to cold rolling deformation and heat treatment steps sequentially so as to obtain the fine-grain tin-phosphor bronze alloy strip;
• wherein, the average grain size of the pretreated tin-phosphor bronze alloy strip is 1-3 μm;
• wherein, the fine-grain tin-phosphor bronze alloy strip comprising the following elements in percentage by mass:
• 4.0-10 wt % of Sn, 0.01-0.3 wt % of P and the balance of Cu and inevitable impurity elements, wherein, the average grain size of the tin-phosphor bronze alloy strip is 1-3 μm, the grain size is in normal distribution, and the standard deviation of the grain size is 0.9 μm or below;
• the proportion of the total low-ΣCSL grain boundary in the tin-phosphor bronze alloy strip in the whole grain boundary is 66-74%, and in the total low-ΣCSL grain boundary, the ratio range of (Σ9+Σ27)/Σ3 is 0.12-0.23:1;
• the deformation amount of the cold rolling deformation step is 15-25%;
• the temperature of the heat treatment step is 600-750° C.;
• the heat preservation time of the heat treatment step is 40-120 s;
• the preparation method further comprises a preparation process flow of the pretreated tin-phosphor bronze alloy strip, which comprises a batching step, a horizontal continuous casting step, a homogenization annealing step, a face milling step, a cold rolling cogging step, a first recrystallization annealing step, an intermediate rolling deformation step, a second recrystallization annealing step, a finish rolling deformation step, a third recrystallization annealing step, a bottom reservation rolling step, and a fourth recrystallization annealing step carried out sequentially, wherein the temperature of the homogenization annealing step is 650-690° C.;
• the temperature of the third recrystallization annealing step is 430-460° C., and the heat preservation time of the third recrystallization annealing step is 1-4 h;
• the temperature of the fourth recrystallization annealing step is 380-430° C., and the heat preservation time of the fourth recrystallization annealing step is 1-4 h;
• the atmosphere for the first recrystallization annealing step, the second recrystallization annealing step, the third recrystallization annealing step, and the fourth recrystallization annealing step is a mixed gas of nitrogen and hydrogen;
• the mixed gas comprises 15-30% of H2 and 70-85% of N2 in percentage by volume;
• wherein, the temperature of the heat treatment step is 600-750° C.