先进材料疑固实验室 Secondary arm spacing Laboratory of Advanced Materials Solidification 104 (E) 102 102 104 106 t:(s) Figure 4.17:SECONDARY SPACING AS A FUNCTION OF SOLIDIFICATION TIME.The best-fit curve to the experimental points for Al-4.5wt%Cu alloy over a wide range of solidification conditions shows that the secondary spacing varies approximately as the cube root of the local solidification time.The latter is defined as the time during which each arm is in contact with liquid (figure 4.1), and is therefore a function of the growth rate,the temperature gradient,and the alloy composition.The secondary spacing is important since,together with Aj, this determines the spacing of precipitates or porosity and thus has a considerable effect on the mechanical properties of as-solidified alloys (figure 1.2).[T.F.Bower, H.D.Brody,M.C.Flemings:Transactions of the Metallurgical Society of AIME 236 (196618241 上游文通大学 SHANGHAI JIAO TONG UNIVERSITYSecondary arm spacing