This paper investigates long fatigue life characteristics of AlSi10Mg and AlSi7Mg aluminium alloys produced using direct metal laser sintering. An inhouse built ultrasonic fatigue testing machine was used to carry out fatigue tests on specimens machined from heat-treated AlSi10Mg and AlSi7Mg alloys subjected to constant fully reversed tension-compression loadings. The fatigue life data acquired for these two additive manufacturing (AM) aluminium alloys were compared with previously published data under heat treatment and nonheat treatment conditions. It was found that fatigue data of tested specimens fit more closely the data of specimens without any heat treatment. Fatigue test results indicate that effects of heat treatment on high cycle fatigue (HCF) and very high cycle fatigue (VHCF) performance of AM alloys should be further investigated in the context of the microstructural changes.

High cycle fatigue (HCF) in the range of 10 6 to 10 8 cycles and very high cycle fatigue (VHCF) in the range of 10 8 to 10 10 cycles are key design criteria for aerospace, automotive, military, transportation, and other industries. However, data gathering in the HCF and VHCF ranges is inefficient with traditional 50to 100-Hz servo-hydraulic testing machines. The development of high power piezoceramic actuators makes it possible to reliably conduct HCF and VHCF tests within a very short time frame at high frequency on the basis of the ultrasonic fatigue testing approach. An ultrasonic fatigue test machine operating in an axial mode shape of test specimens at 20 kHz was designed and built to investigate VHCF characterization of lightweight metal alloys. The experimental setup went through several stages of design and validation. Finite element analysis was employed to design three versions of an acoustical horn, a single half wavelength booster, and three types of nonferromagnetic samples. The developed ultrasonic fatigue machine was used to conduct fatigue testing of specimens made from 2024-T351 and 7075-T6 aluminum alloys to generate representative HCF and VHCF data. HCF and VHCF data for these alloys were found to be in good agreement with experimental fatigue data from the literature.

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