Hot dwell-fatigue behaviour of additively manufactured AlSi10Mg alloy: Relaxation, cyclic softening and fracture mechanisms

This paper presents the results of high temperature strain-range controlled low cycle fatigue tests of a laser powder bead fused AlSi10Mg alloy. Following stress relief (2hrs at 300 ℃), two cyclic loading waveforms (standard triangular and dwell-type trapezoidal waveforms) and three temperatures (100 ℃, 250 ℃ and 400 ℃) were applied to investigate both the mechanical response and the related microstructural changes of this additively manufactured (AM) aluminium alloy. The bulk mechanical responses were found to exhibit a continuous cyclic softening, decreasing stress relaxation and decreased energy dissipated per cycle. The stress relaxation is strongly affected by the test temperature rising to almost complete relaxation at 400 ℃. At lower temperatures (100 ℃ and 250 ℃), the higher the temperature the more subgrains are developed during cyclic loading. Up to 250 ℃, the subgrain size increases with temperature and laser powder bead fused defects pref­erentially act as the fatigue crack initiation sites. While at 400 ℃, coarse Si particles precipitate during cyclic deformation and a high density of microvoids are nucleated from these coarse Si precipitates, which grow and link up to cause failure, resulting in a dimple dominated ductile fracture.Jianguang Bao, Professor Adil Benaarbia and Professor Wei Sun would like to acknowledge the China Scholarship Council for the sponsorship of the PhD project for Jianguang Bao. Financial support through the Joint Fund of Large-scale Scientific Facility of National Natural Science Foundation of China (U2032121) is gratefully acknowledged. Sincere thanks are also due to Professor Yanan Fu from the SSRF for her technical assistance on performing the SR- μ CT exper­imental setup, and to Mr Shane Maskill at the University of Nottingham for his support during LCF tests. The Manchester (Henry Moseley) X-ray Imaging Facility was funded in part by the EPSRC (grants EP/F007906/1, EP/F001452/1 and EP/M010619/1)