## 1 Introduction
[15] studied the tensile properties of EBPP Ti6 Al4V parts manufactured using two different themes and built along several orientations. The quasi-static and dynamic properties of as-built Ti6 Al4V parts prepared by 3D laser deposition technology and produced with different orientations were investigated in [PERSON] et al. [16]. The static tensile properties of AM Ti6 Al4V parts exposed to different heat treatment cycles were published in references [17; 18; 19; 20]. The as-built LPBF Ti6 Al4V parts are characterised by high process-related residual stresses and a needle-like-shaped \(\alpha\)'-acicular martensitic microstructure. These two factors normally cause an increase in hardness and strength of the parts but at a cost of reduction in ductility [18; 19]. Thus, to optimise the strength and ductility of LPBF Ti6 Al4V for structural application, the parts are exposed to post-process heat treatment [17]. A review of the aforementioned studies suggests that the research has mostly focused on the static mechanical properties of as-built AM Ti6 Al4V parts. The influence of build orientation on tensile static properties has also been widely investigated, with studies showing isotropy in these properties of LPBF parts [21; 22]. However, the effects of quasi -static strain rates on different microstructures of AM Ti6 Al4V(ELI) produced by different post-process heat treatment strategies are lacking in the literature [13; 14; 15; 16; 17; 18; 19; 20]. Typically, the equilibrium microstructure of the AM Ti6 Al4V alloy contains a large amount of \(\alpha\)-phase with a hexagonal-closed-packed (HCP) structure and a small fraction of \(\beta\)-phase with a body-centred cubic (BCC) structure [23]. It also exists in different stable microstructures, namely lamellar, equiaxed, bimodal and Widomastatten microstructures, based on the heat treatment, residence time and the cooling rate adopted [23]. The mechanical performance of Ti6 Al4V depends on the type of microstructure as well as the intrinsic microstructural variables, such as crystallographic texture, grain size and levels of defects (mainly dislocation density) [24]. The high cycle fatigue strength and optimal static properties of this alloy have been shown to increase in the order of equiaxed, lamellar and bimodal microstructures [25]. However, intrinsic microstructural parameters, such as fraction and size of primary \(\alpha\) in bimodal microstructure, diameter of equiaxed \(\alpha\)-grains in equiaxed microstructure and the thickness of \(\alpha\)-laths in lamellar microstructure, have been found to have profound influence on these mechanical properties [25; 26]. In the present study, the compressive quasi-static mechanical properties of different microstructures of LPBF Ti6 Al4V(ELI) at different strain rates were investigated. The as-built samples were first stress relieved to alleviate the macro-scale residual stresses. Subsequently, the stress-relieved microstructure of DMLS Ti6 Al4V(ELI) was modified through different heat treatment strategies. Scanning electron microscopy (SEM) was used to study the microstructure and crystallographic texture of the obtained parts. A universal testing machine (UTM) was used to investigate the mechanical behaviour of the different heat-treated microstructures of the alloy at different quasi-static strain rates and at ambient temperature.