The Evolution of Microstructure, Mechanical Properties and Fracture Behavior with Increasing Lanthanum Content in AZ91 Alloy

Di Tie,Zhanyong Zhao,Renguo Guan,Xiaopeng Lu,Jufu Jiang,Minfang Chen,Yi Jiang,Fei Gao

doi:10.3390/met10091256

Abstract

AZ91 alloy is a widely applied commercial magnesium alloy due to its good castability, balanced mechanical properties and acceptable price, and lanthanum alloying has been proven to be one of the most effective methods to further improve its mechanical properties. Therefore, we reveal the evolution of microstructure, mechanical properties and fracture behavior with increasing lanthanum content in AZ91 alloy in this study. The magnesium matrix was significantly refined by lanthanum content, and this effect became more evident with increasing addition of lanthanum. The presence of Al3La precipitates significantly reduced the grain mobility and suppressed the formation of Mg17Al12 discontinuous precipitates along the grain boundaries. The rheo-cast alloys exhibited improved and balanced tensile strength and ductility after aging treatment. The fracture type of AZ91-La alloys could be classified as ductile fracture due to the presence of less quasi-cleavage planes and more dimples with a mixture of tear ridges and micropores. Due to the fully refined microstructure and the balanced mechanical properties, the AZ91–1.0La (mass%) alloy presented the greatest potential for industrial applications among the three studied AZ91-La alloys.

Highlights

IntroductionThe application of magnesium alloys appropriately meets the demand for lightweight heat dissipation materials including electronic components, vehicle parts and heat sink components, which has increased in recent years [4,5,6]
Magnesium alloys have been widely applied in automotive, aerospace and biomedical industries, which can be attributed their low density, high specific strength and good castability [1,2,3].The application of magnesium alloys appropriately meets the demand for lightweight heat dissipation materials including electronic components, vehicle parts and heat sink components, which has increased in recent years [4,5,6]
The magnesium matrix was significantly refined by lanthanum content, and this effect became more evident with increasing amounts of added lanthanum

Summary

Introduction

The application of magnesium alloys appropriately meets the demand for lightweight heat dissipation materials including electronic components, vehicle parts and heat sink components, which has increased in recent years [4,5,6]. Among the various cast magnesium alloys, AZ91 alloy became one of the most widely used cast magnesium alloys due to its outstanding castability and aging hardenability [7,8]. Despite these advantages, AZ91 alloy still has some other limitations, including low ductility, insufficient formability, low Young’s modulus and poor corrosion resistance, which narrow its industrial applications [9,10]. The improvement of AZ91 alloy’s comprehensive performance, especially its mechanical properties, has become a research focus in recent years.

Methods

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Discussion

Conclusion