EFFECT OF COOLING RATE ON THE GRAIN REFINEMENT OF MG-3Nd ALLOYS BY ALUMINUM

The effect of cooling rate on the grain refinement of Mg-3Nd alloys refined by Al was investigated in this work. The experimental results show that the grain size of Mg-Nd alloys can be refined by increasing the cooling rate and the Al addition. When the content of Al is more than 2%, Al2Nd particles can be observed inside the grains, which can be act as an effective nucleating site. The orientation relationship between Al2Nd particles and alpha-Mg matrix is determined as [101](Al2Nd) parallel to [(1) over bar 100](Mg), ((2) over bar 22)(Al2Nd) parallel to (0002)(Mg) and [(1) over bar 11](Al2Nd) parallel to [0001](Mg), (02 (2) over bar)(Al2Nd) parallel to (01 (1) over bar0)(Mg) by TEM analysis. The refining effect is affected by the size and the number density of Al2Nd particle. The minimum nucleating size of observed Al2Nd particle in Mg-3Nd-2Al and Mg-3Nd-3Al alloys decreases with increasing the cooling rate, which are 1.5 and 1 lm, when the cooling rate is 1.2 and 3.5 degrees C/s, respectively. The number density of Al2Nd particle in Mg-3Nd-2Al alloy increases with increasing the cooling rate from 0.3 to 1.2 degrees C/s and decreases with further increasing the cooling rate to 3.5 degrees C/s. And the number density of Al2Nd particle in Mg-3Nd- 3Al alloy increases with increasing the cooling rate.