Grain-Refined Microstructure and Hard Surface Layer Produced by SMRGT Process for Improved Corrosion Behavior of Mg-3Al-
- PDF / 7,677,035 Bytes
- 10 Pages / 593.972 x 792 pts Page_size
- 82 Downloads / 152 Views
ÓASM International 1059-9495/$19.00
Grain-Refined Microstructure and Hard Surface Layer Produced by SMRGT Process for Improved Corrosion Behavior of Mg-3Al-1Zn Alloy Biqiang Chen, Chao Xin, Guifeng Zhang, Fan Zhou, and Linjie Zhang (Submitted June 12, 2018; in revised form December 18, 2018; published online January 22, 2019) To improve the surface properties and performance, a grain-refined surface layer was produced on AZ31B Mg alloy by a newly developed surface nano-crystallization and hardening process called surface mechanical rolling grinding treatment (SMRGT). The grain size refinement and minimal surface hardening were confirmed by the microstructure observations, XRD results and microhardness tests and were attributed to the multipass small strain-induced plastic deformation of the material during the SMRGT process. A nano-grain surface layer (average grain size of 100 nm) and a graded microhardness variation (average 113 HV adjacent to surface) along the thickness direction were generated. The Ecorr values of the as-SMRGTed samples were 2 1.43 ± 0.03 and 2 1.42 ± 0.02 V, increasing by 30-40 mV compared with the values of the as-received (AR) sample (2 1.46 ± 0.02 V), corresponding to icorr ranging from 3.0 3 1025 to 1.0 3 1025 and 5.0 3 1026 A/cm2, respectively. Charge transfer resistance (Rct) increased from 93.4 to 292.4 and 578.3 X ( 3-6 times) with the increasing number of SMRGT passes. The corrosion resistance improvement was attributed mainly to the dramatic strain-induced surface grain refinement and minimal surface hardening that give rise to a more smooth and densely packed surface state. Keywords
electrochemical corrosion, nanoscale surface layer, surface state, transmission electron microscopy (TEM)
1. Introduction Mg and its alloys exhibit excellent specific strength and low density, and they can be used in many lightweight applications including aerospace components, computer parts, handheld tools and automobile parts (Ref 1, 2). Because its elastic modulus (40-45 GPa) is closer to that of human bones (10-40 GPa), Mg alloys are also candidate materials for bone implants and stent applications, offering less invasive repair and temporary support during tissue recovery. The use of Mg alloys would reduce the stress-shielding phenomena caused by currently used the metallic implants (stainless steel or Ti alloy) (Ref 3). As degradable materials, Mg and its alloys offer the possibility of better physiological repair and reconstruction with minimum inflammatory response (Ref 4). As reported in Ref 5, the cytotoxicity evaluation tests indicate that Mg-1Al, Mg-1Sn and Mg-1Zn alloy are highly compatible with cell. However, the key factors to limit a wider use of Mg and its alloy can be summarized as follows: (a) difficulties in processing; (b) relatively low strength and ductility; and (c) high susceptibility to corrosion in many environments (Ref 68). Among these factors, the unsatisfactory corrosion perforBiqiang Chen, Chao Xin, Guifeng Zhang, Fan Zhou, and Linjie Zhang, State Key Laboratory for Mec
Data Loading...
