Fatigue behaviour of cast magnesium alloy AZ91 microstructurally modified by friction stir processing

Abstract

A B S T R A C T Friction stir processing (FSP) was applied to cast magnesium alloy AZ91-F to modify the as-cast microstructure, and the effect of FSP on fatigue behaviour was discussed based on microstructural consideration, crack initiation, crack growth behaviour, and fracture surface analysis. Fully reversed axial fatigue tests have been performed using as-cast, T5-aged and their FSPed specimens (as-cast/FSP and T5/FSP). It was found that both FSPed specimens exhibited significantly higher fatigue strength than the as-cast and T5-aged specimens. FSP resulted in the break-up of coarse as-cast microstructure, grain refinement of the matrix, finely dispersed precipitates and increase of hardness, thereby both the crack initiation resistance and the crack growth resistance were considerably enhanced compared with the as-cast and T5-aged specimens, resulting in the improved fatigue strengths of the FSPed specimens.

Magnesium alloy defectology AZ91D high‐pressure die cast and influence on the fatigue behaviour

“…The principal factors in metallurgical defects are alloy composition, dissolved gas content, entrained solids (such as oxides and inclusions, such as inter‐metallic compounds) and improper temperatures. The results can be poor fluidity, die soldering, shrinkage porosity, hot cracking and gas porosity . This section is focused on the identification of different types of metallurgical defects occurring in alloy AZ91D HPDC and its influence on fatigue behaviour.…”

“…The results can be poor fluidity, die soldering, shrinkage porosity, hot cracking and gas porosity. 18 This section is focused on the identification of different types of metallurgical defects occurring in alloy AZ91D HPDC and its influence on fatigue behaviour.…”

“…In past works, the microstructure‐affected micromechanisms of fatigue crack growth in Mg high‐pressure die‐casting alloys manifested by the effects of dendrite cell size, interdendritic Al‐rich solid solution layer and surface segregation phenomena have been studied . Recently, the fatigue behaviour of AZ91 magnesium alloy has been studied, focusing on different types of processes and heat treatments …”

“…13 Recently, the fatigue behaviour of AZ91 magnesium alloy has been studied, focusing on different types of processes and heat treatments. [14][15][16][17][18] The aim of the present study is to identify casting defects present in this AZ91D high-pressure die-casting alloy and to analyse and evaluate the influence of and correlation between each casting defect type and the fatigue behaviour to obtain adequate properties of the material that will be used. This paper has been carried out by conducting a series of fatigue tests using AZ91D samples that were manufactured using the same casting technique as inservice components to reproduce the same surface conditions for the specimens as for the in-service components.…”

Effect of friction stir processing parameters on the microstructural and electrical properties of copper

“…Furthermore, a large number of works have also addressed the surface modification of cast substrates. Grain refinement, dissolution of strengthening phases and removal of cast porosities were the main improvements achieved by using these techniques for processing sand cast aluminium [15][16][17][18][19] and magnesium alloys [20].…”