 The study investigates the complex thermal histories in additive manufacturing, AM, of titanium alloy and their influence on microstructural evolution, layer bands formation, and micro-hardness. A thermal model is calibrated using part-scale blocks fabricated on differently sized substrates to establish a relationship between key microstructural characteristics and thermal cycling. Results show that temperature ranges just underneath the transverse temperature control the different band distributions at the center and corner of the blocks and alpha sizes in the normal region are linked to integral areas obtained from thermal curves. The study further demonstrates that alpha coarsening during thermal cycles is primarily driven by multi-dissolution and precipitation transformations instead of austral ripening, establishing a quantitative thermal microstructure-micro-hardness relationship helpful for microstructural design in AM. This article was authored by Xu Feilu, Guahao Zhong, Junjie Li, and others.