Fracture toughness of L-PBF fabricated aluminium–silicon: a quantitative study on the role of crack growth direction with respect to layering

Abstract

Laser powder bed fusion has become one of the major techniques within metal additive manufacturing, especially when delicate structures and high geometric accuracy are concerned. Lately, the awareness of the material-specific macroscopic anisotropy has risen and led to widespread investigations on the static mechanical strength. However, little is known about the fracture behavior of the layer-wise fabricated metal components and their affinity of crack propagation between consecutive layers, which is particularly important for aluminium-silicon alloys containing embrittled zones in double-irradiated areas. A recent study indicated that there is a significant drop in fracture toughness in case the crack growth direction is parallel to the layering. To investigate this matter further and to shed light on the fracture toughness behavior in the range of a 0°-45° angle offset between the crack growth direction relative to the layering, notched samples with varying polar angles were subjected to mode I fracture toughness testing. Our results indicate that the fracture toughness is an almoststable characteristic up to a mismatch of about 20° between the crack propagation path and the layering, at which point the fracture toughness decreases by up to 10%.

Fracture resistance of AlSi10Mg fabricated by laser powder bed fusion

“…Yet, studies of LPBF-produced Al-Si alloys are scarce. The reported fracture toughness values in literatures [3,[24][25][26] are in the range of 40-60 MPa√𝑚. These numbers, although significantly higher than values of cast Al-Si alloys, e.g., AlSi7Mg has been reported with a fracture toughness of 20-28 MPa√𝑚 [27], may be somewhat elevated as a result of sample size effects [3] and/or a lack of fatigue precracking [24][25][26] prior to testing.…”

“…The reported fracture toughness values in literatures [3,[24][25][26] are in the range of 40-60 MPa√𝑚. These numbers, although significantly higher than values of cast Al-Si alloys, e.g., AlSi7Mg has been reported with a fracture toughness of 20-28 MPa√𝑚 [27], may be somewhat elevated as a result of sample size effects [3] and/or a lack of fatigue precracking [24][25][26] prior to testing. Furthermore, the size independent fracture toughness values calculated from the recent work by Liu et al [28] on the LPBF AlSi10Mg are comparable (27)(28)(29)(30)(31) with cast material.…”

Heat Treatments and Critical Quenching Rates in Additively Manufactured Al–Si–Mg Alloys

“…Compared to the aluminum solid solution (α-Al), the Si-segregations are brittle and prone to shear fracture [8]. Due to the layer-wise building approach in the LPBF process, these embrittlements repetitively occur every single layer and become the governing weakness, defining the observable macroscopic properties, as has been documented for tensile and compression strength as well as for the fracture toughness [8][9][10][11][12]. Even though these weaknesses are present, LPBF Al-Si-Mg alloys exhibit superior mechanical properties compared to their cast counterparts, at least under static loading, while the fatigue performance suffers from surface roughness and sub-surface defects [13,14].…”