Fatigue properties of Scalmalloy® processed by laser powder bed fusion in as-built, chemically and conventionally machined surface condition

Abstract

Additive manufacturing of metallic parts via laser powder bed fusion has is attractive for applications such as aerospace engineering due to the high weight-saving potential, which is based on the ability of the process to produce complex designs. The aluminum alloy Scalmalloy® can increase this potential for lightweight design further with its high strength and high ductility. These advantages already led to a variety of use cases for statically loaded parts. Research on the dynamic mechanical behavior of Scalmalloy® is far less extensive than for other aluminum materials such as AlSi10Mg. There is limited insight into the fatigue behavior and mechanisms of Scalmalloy® in as-built and various surface-finished states. This study aims to understand the fatigue-fracture mechanisms of Scalmalloy® not only in two different as-built surface conditions but also in machined and chemically milled surface states. Fatigue specimens with four different surface modifications were produced, their surface morphology was characterized and correlated to the fatigue performance. Fractographic analysis was conducted to reveal the fracture-inducing defects. Defect-based modeling is shown to describe the influence of defect size on the fatigue behavior and verifies that the fatigue properties are independent of sample size. Kitagawa-Takahashi-diagrams are drawn upon to explain the influence of defect size, and an equivalent initial flaw size (EIFS) was defined and coupled to an El-Haddad-type model to arrive at a unified model predicting the fatigue strength for all four surface conditions despite their differences in defect nature.