Effect of Hatch Spacing on Microstructure, Defect Formation and Properties of Additively Manufactured A7075 Alloy

Understanding the mechanisms of microstructure evolution and defect formation, and their influence on mechanical properties and fracture mechanisms (from crack initiation to failure stage), is essential for manufacturing high-strength, fatigue-resistant A7075 alloy by selective laser melting (SLM). In this investigation, the A7075 alloy was fabricated using a laser power of 350 W with various hatch spacings of 1.0, 1.5, and 2.0 μm, and scanning speeds of 800, 1100, and 1300 mm/s. The results show that the alloy exhibits an equiaxed grain structure, which varies from coarse grains at small hatch spacing and low scanning speed to fine grains with increasing hatch spacing and scanning speed. The alloys exhibit low tensile strength due to solidification cracking and pores. However, this tensile strength increases with hatch spacing, while it decreases with scanning speed. At small hatch spacing and low scanning speed, fracture occurs through the coalescence of pores and solidification cracking along the weakly bonded grain boundaries (GBs) due to eutectic growth along these boundaries. In contrast, with increasing hatch spacing and scanning speed, fracture occurs through solidification cracking and coalescence of pores. This research provides valuable insights into the microstructure evolution, defect formation, and fracture mechanisms of the A7075 alloy under common processing conditions.