Influence of substrate microstructure on defect formation during Al alloy laser powder bed fusion

Abstract

Laser powder bed fusion (PBF-LB) produced aluminium alloy components have attracted growing attention over the past two decades due to their lightweight nature and excellent thermal and corrosion properties. However, few studies have examined the impact of substrate composition and microstructure. Using a high-performance Al-Ni-Ce-Mn-Fe alloy (PA1) designed for additive manufacturing, we performed a series of single-track PBF-LB experiments on as-cast PA1 and as-rolled Al6061 substrates to study their impact on track quality. Microstructural analysis shows that, in optimal conditions, PBF-LB of PA1 produces very fine eutectic cells (∼200 nm) without defects. Conversely, the as-cast PA1 substrate contains large columnar intermetallics, which have a strong influence on defect formation during PBF-LB during initial layers. Such influence diminishes with increasing build height due to microstructure homogenisation. However, the identified intermetallic-induced (IM) pore formation suggests a broader relevance beyond the present system, such as alloys form intermetallic under AM conditions or additive repair. We reveal and quantify the effects of print parameters and substrate microstructure on defect formation during PBF-LB of PA1 using high-speed synchrotron X-ray imaging. Our results show a new defect type, termed intermetallic-induced pores, arising from interactions between the keyhole and the pre-existing intermetallics. By quantifying different melting modes and defect types, we establish a process map and propose defect-lean printing strategies for PBF-LB of PA1.