## 3 Results and Discussions
### Quasistatic Behavior  
The quasistatic behavior of the three conditions of the pure Al4047 parts and two hybrid batches, wrought Al7020 + SLM Al4047, is shown in the form of stress-strain curves in Figure 5. The quasistatic tensile strength of the as-built condition, batch A, has been found highest from the pure Al4047 with an ultimate tensile strength value of 418.9 \(\pm\) 9.6 MPa with an accompanying total strain at fracture of 3.91 \(\pm\) 0.27 [10\({}^{-2}\)]. After stress-relief treatment in batch B, the ultimate tensile strength decreased to 372.3 \(\pm\) 7.2 MPa, and the corresponding fracture strain also decreased to a value of 3.41 \(\pm\) 0.29 [10\({}^{-2}\)].  
The combination of the two thermal treatments in batch C decreased the ultimate tensile strength further to 361.1 \(\pm\) 3.4 MPa but with an increase in fracture strain to 4.05 \(\pm\) 0.15 [10\({}^{-2}\)]. The stress-strain curves in Figure 5 show the influence of processing configurations on mechanical behavior. Tensile strength decreased due to stress-relief treatment as well as due to base plate heating during the process. There is a simultaneous decrease in the ultimate tensile strength and fracture strain due to post-process stress-relief; whereas, a decrease in ultimate tensile strength due to in-process base plate heating is accompanied with a corresponding increase in fracture strain. This effect can be characterized on the basis of dendritic width to Hall-Petch behavior where the microstructure is coarsened due to decreased thermal gradients, owing to base plate heating. Along with the phenomenon of grain boundary strengthening, other factors, like porosity and Si solubility, play their own role. Increased porosity decreases the tensile strength as well as fracture strain. Si having a very low solubility of 1.65% at the eutectic temperature is reduced to only 0.06% when temperature reduces to 200 \({}^{\circ}\)C; however, the Si solubility in Al increases when the cooling rates are high. About 10% of free Si exists in Al4047 cast material, reducing to only about 1% in SLM-processed part [6]. The increase in strength is accredited to increased solubility where Si is entrapped in the matrix giving strength to it and reducing Si rejection,  
Figure 5: Characteristic stress-strain curves for Al4047 specimens: as-built batch A; stress-relieved batch B; base plate heated and stress-relieved batch C; the as-built hybrid batch D; and, stress-relieved hybrid batch E.  
which could have increased the brittleness, which resulted in marginally less decrement of fracture strain when compared with a significant increase in ultimate tensile strength with reference to cast alloy [45].  
Ultimate tensile strength value of the hybrid specimens (wrought Al7020 + SLM Al4047) in the as-built condition (batch D) turned out to be 312.4 \(\pm\) 12.8 MPa with a corresponding fracture strain of 5.8 \(\pm\) 0.57 [10\({}^{-2}\)]. The standard deviation of these values was much more as compared to those of pure Al4047 specimens, and the dominant fracture mechanism was from the interface between the wrought and SLM part. After stress-relief of these specimens, the ultimate tensile strength decreased to 316 \(\pm\) 7.60 MPa and the fracture strain increased to 11.7 \(\pm\) 0.21 [10\({}^{-2}\)]. The high increase in fracture strain as compared to a small decrease in ultimate tensile strength was due to a shift in the fracture mechanism from the interface to the pure Al7020 part of the material.