Fatigue Properties of AZ31B Magnesium Alloy Processed by Equal-Channel Angular Pressing

Ryuichi Yamada,Shoichiro Yoshihara,Yasumi Ito

doi:10.3390/met11081191

Ryuichi Yamada, Shoichiro Yoshihara + Show 1 more

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https://doi.org/10.3390/met11081191

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Abstract

A stent is employed to expand a narrowed tubular organ, such as a blood vessel. However, the persistent presence of a stainless steel stent yields several problems of late thrombosis, restenosis and chronic inflammation reactions. Biodegradable magnesium stents have been introduced to solve these problems. However, magnesium-based alloys suffer from poor ductility and lower than desired fatigue performance. There is still a huge demand for further research on new alloys and stent designs. Then, as fundamental research for this, AZ31 B magnesium alloy has been investigated for the effect of equal-channel angular pressing on the fatigue properties. ECAP was conducted for one pass and eight passes at 300 °C using a die with a channel angle of 90°. An annealed sample and ECAP sample of AZ31 B magnesium alloy were subjected to tensile and fatigue tests. As a result of the tensile test, strength in the ECAP (one pass) sample was higher than in the annealed sample. As a result of the fatigue test, at stress amplitude σa = 100 MPa, the number of cycles to failure was largest in the annealed sample, medium in the ECAP (one pass) sample and lowest in the ECAP (eight passes) sample. It was suggested that the small low cycle fatigue life of the ECAP (eight passes) sample is attributable to severe plastic deformation.

Highlights

Ischaemic heart disease is the world’s biggest killer, accounting for a combined 9.4 million deaths in 2016 [1]
Elongation to failure was larger in the ECAP-8 p sample than than in the annealed sample
Elongation to failure was larger in the ECAP-8 p sample than in the annealed sample

Summary

Introduction

Ischaemic heart disease is the world’s biggest killer, accounting for a combined 9.4 million deaths in 2016 [1]. A stent, as a countermeasure against ischaemic heart disease, is employed to expand a narrowed tubular organ, such as a blood vessel. Once the stainless steel stent is implanted, it will remain in an artery permanently because of its excellent corrosion resistance. Restenosis is when too much tissue grows around the stent. This could narrow or block the artery again. The mechanical strength and properties of magnesium are suitable for biodegradable implants, especially for stent application. Pulsatile pressure and repetitive mechanical forces within the coronary artery may result in fatigue fracture after stent implantation, in patients with complex coronary disease [7]. It has been reported that stents implanted near the heart have a higher probability of fatigue failure. If the fatigue properties can be improved, there is a possibility of reducing the corrosion rate

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