供桌的摆放:300分工科材料类英文论文求好翻译.2

(1) Discontinuous coarsening mechanism.It was previously found that spinodal decomposition firstly occurred in the solution-treated Al-Zn-(Cu) alloys held at 2500C for different time, which
was slightly below the eutectoid temperature; thenthe spinodal microstructure transformed into the fine lamellar one by DP DP completely ended in 30 min in AlZn alloy, while in 20 min in AlZn-2Cu alloy [5].However, the fine larneflar microstructure was still unstable. When the sample of AlZn alloy was held at
250℃ for 2 h, discontinuous coarsening (DC) cells formed at the primitive boundaries and cellular boundaries of DP (figure 1(a)). With the increase of aging time, discontinuous coarsening cells swal-lowed up the fine lamellar microstructure by the mi-
gration of cellular boundaries with high angle, and then the sample became the coarsening cellular dual phase microstructure. At the same time, new discontinuous coarsening cells continually formed at the high angle grain boundaries (figure 1(b)). With the
further increase of aging time, the fine lamellar microstructure was replaced by the coarsening lamellar one (figure 1(c)). When the sample of AlZn-2Cu was kept at 250℃, the fine lamellar microstructure of DP similarly changed into the coarsening lamellar one through discontinuous coarsening, but the
transformation velocity was slower than that in the AIZn alloy (figure 1(d)). The microstructure evolution of the sample aged at 200℃ was the same as that of the sample aged at 250℃ in the AlZn-(Cu) alloy, i.e. by the discontinuous coarsening mecha-
nism of nucleation and growth.(2) Dissolution and spheroidization mechanism.In the AI-Zn-(Cu) alloy aged at 150℃ for 5 h after solution treatment, DP transformation had al-
ready finished, and the fine lamellar microstructure
of DP was dissolved into the short rod-shaped one,whose size was relatively large at the original boundaries and cellular boundaries (figure 2(a)).The rod-shaped microstructure with large size around and at the boundaries increased and gradu-
ally changed into the spherical one with the increase of aging time (figure 2(b)). With the further extension of aging time,the rod-shaped microstructure inside the DP cell also gradually changed into the spherical one, so that fine Zn particles dispersedly distributed at the Al matrix (figure 2(c)). When the
sample of AIZn-2Cu alloy was kept at 150℃, the
microstructure evolution was similar to that in the
AlZn binary alloy, but the third phase was observed
in the ternary alloy (figure 2(d)), which was the
metastable CuZn4 phase testified by X-ray diffrac-
tion analysis. With the increase of aging time, the
CuZn4 phase gradually transformed into the
A14Cu3Zn phase and finally completely transformed
into the A14Cu3Zn phase.