For indirect reactions involving more than one intermediate complex from reactant valley to product valley, the reaction dynamics becomes very complicated for researchers due to competition between pathways. In order to resolve the large discrepancy between theoretical and experimental studies on the linear or bent structures of complexes involved in the title endothermic reaction, we performed a crossed-beam experiment at a large collision energy (Ec) range with mapping of the velocity distributions of Al reactants and AlO products. We found that the reaction proceeds through different complex-forming mechanisms with the increase of Ec: at low Ec near the reaction threshold, only low impact-parameter collisions contribute through a collinear Al-OCO short-lived complex, and at high Ec, the bent-structure complexes, formed by either isomerization or noncollinear collisions, come into play.