Effect of a high magnetic field on the growth of the alpha-Al dendrite in three Al-based alloys during directional solidification at a higher growth speed has been investigated experimentally. It has been found that for different alloy, the effect of the magnetic field on the growth of the alpha-Al dendrite is different. Indeed, a high magnetic field has caused the occurrence of the columnar-to-equiaxed transitions (CET) of the alpha-Al dendrite in the Al-Si alloy. However, for the Al-Ni alloy, the effect of the magnetic field on the alpha-Al dendrite is negligible. Further, the thermoelectric magnetic force (TEMF) imposed on the dendrite under a high magnetic field has been investigated numerically and the results show that the value of the TEMF imposed on the dendrite during directional solidification under a 10 T high magnetic field is about 10(5) N/cm(3) and this force should be responsible for the occurrence of the CET in the Al-Si alloy. This may act as an experimental proof that the force imposed on the dendrite will induce the occurrence of the CET. Above results are discussed from the TEMF imposed on the dendrite and the difference of the stacking fault energy of alpha-Al dendrites in the different alloy. (C) 2009 Elsevier B.V. All rights reserved.