Effect of a Minor Sr Modifier on the Microstructures and Mechanical Properties of 7075 T6 Al Alloys

Shaoming Ma,Huiyuan Wang,Youhong Sun,Chi Zhang,Baochang Liu,Yinlong Ma,Ming Qian,Xiaoshu Lü

doi:10.3390/met7010013

Shaoming Ma, Huiyuan Wang + Show 6 more

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https://doi.org/10.3390/met7010013

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Abstract

The influence of a minor strontium (Sr) modifier on the microstructures and mechanical properties of 7075 Al alloys was investigated in this paper. The grain size of cast 7075 Al alloys was refined from 157 μm to 115 μm, 108 μm, and 105 μm after adding 0.05 wt. %, 0.1 wt. %, and 0.2 wt. % Sr, respectively. The extruded 7075 Al alloys was refined with different degrees of Sr modifier. The mechanical properties were optimum when adding 0.1 wt. % Sr. The ultimate tensile strength (σb) increased from 573 to 598 MPa and the elongation-to-failure (δf) was raised from 19.5% to 24.9%. The microhardness increased from 182 to 195 Hv. The tensile fracture surface via scanning electron microscopy (SEM) revealed a transition from brittle fracture to ductile fracture as Sr increased from 0 wt. % to 0.2 wt. %. The result in this paper proved that the modifier can improve the properties of 7075 Al alloy.

Highlights

The insufficient mechanical properties of conventional steel drill pipes pose a challenge to the deep and ultra-deep well industry because of the high density of steel
alloy drilling pipes (ADP) has been successfully applied in some world record deep wells, such as SG-3 in Russia, the BD-04A well in
The goal of the present study is to clarify whether Sr modification has effect on the microstructures and mechanical properties of 7075 Al alloy, reveal the reinforcement mechanism of the Sr modifier preliminarily

Summary

Introduction

The insufficient mechanical properties of conventional steel drill pipes pose a challenge to the deep and ultra-deep well industry because of the high density of steel. High-strength aluminum alloys, such as 7075 and 2024 Al alloy, are preferred over steel for making drill pipes for deep oil and gas wells due to their better strength to weight ratio, lower stiffness, and higher corrosion resistance [1,2]. Aluminum alloy drilling pipes (ADP) have been proved promising for making drilling pipes worldwide, especially in countries such as America, Japan, France, and Russia. The 7075 Al alloy, which is one of the 7000 series (Al–Zn–Mg–Cu) ultra-high strength alloys, have been extensively used for structural components in aerospace and automobile industries [3,4]. Fine-grain strengthening during casting, including ultrasonic vibrations [6,7], electromagnetic stirring [8], and modification [9], is a good way to simultaneously achieve higher tensile strength and ductility for alloys at present

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