In the laser powder bed fusion additive manufacturing process, parameters such as laser scanning speed and power have overarching effects on the development of melt pool and solidification microstructures. In this study, a wide range of energy densities, calculated from the scanning speed, power, and spot size of the laser, have been systematically investigated experimentally and numerically. Melt pool size, and microstructure characteristics, including grain size, orientation and porosity were quantified via optical and scanning electron microscopes. Using a powder packing, transient heat, and fluid flow simulation with considerations of surface tension, evaporation, and multiple laser reflection, the local solidification conditions in terms of thermal gradient and cooling rate were analyzed to interpret the solidification behaviors. A process window driven by experiments, process modeling and solidification analytics were proposed to guide the parameter selection for desired solidification microstructures.