TY - JOUR

T1 - Thixomolded AZ91D and MRI153M magnesium alloys and their enhanced corrosion resistance

AU - Buzolin, Ricardo H.

AU - Volovitch, Polina

AU - Maltseva, Alina

AU - Lamaka, Sviatlana

AU - Blawert, Carsten

AU - Mendis, Chamini L.

AU - Lohmüller, Andreas

AU - Kainer, Karl U.

AU - Hort, Norbert

N1 - Funding Information: Helmholtz‐Zentrum Geesthacht acknowledge the German Ministry of Education and Research for the provision of financial support within the framework of the proposal O2PJ2792 and Neue Materialien Fürth GmbH also acknowledge the German Ministry of Education and Research for the provision of financial support within the framework of the proposal O2PJ2791. Ricardo H. Buzolin acknowledges CD‐Laboratory for Design of High‐Performance Alloys by Thermomechanical Processing for the support by the Christian Doppler Society. Publisher Copyright: © 2020 The Authors. Materials and Corrosion published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

PY - 2020/3/1

Y1 - 2020/3/1

N2 - AZ91D and MRI153M alloys were produced by thixomolding. Their corrosion resistance is significantly higher than that of similar materials produced by ingot or die-casting. A corrosion rate smaller than 0.2 mm/year in 5 wt% NaCl solution is measured for the thixomolded AZ91D alloy. The corrosion behaviour was evaluated using immersion tests, electrochemical impedance spectroscopy, hydrogen evolution, glow discharge optical emission spectroscopy, and atomic emission spectroelectrochemistry. A bimodal microstructure is observed for both alloys, with the presence of coarse primary α-Mg grains, fine secondary α-Mg grains, β-phase, and other phases with a minor volume fraction. The amount of coarse primary α-Mg is significantly higher for the AZ91D compared with the MRI153M. The network of β-phase around the fine secondary α-Mg grains is better established in the thixomolded AZ91D alloy. A combination of several factors such as the ratio of primary to secondary α-Mg grains, localised corrosion or barrier effect due to other phases, as well as regions of preferential dissolution of the α-Mg due to chemical segregation, are thought to be responsible for the high corrosion resistance exhibited by the thixomolded AZ91D and MRI153M.

AB - AZ91D and MRI153M alloys were produced by thixomolding. Their corrosion resistance is significantly higher than that of similar materials produced by ingot or die-casting. A corrosion rate smaller than 0.2 mm/year in 5 wt% NaCl solution is measured for the thixomolded AZ91D alloy. The corrosion behaviour was evaluated using immersion tests, electrochemical impedance spectroscopy, hydrogen evolution, glow discharge optical emission spectroscopy, and atomic emission spectroelectrochemistry. A bimodal microstructure is observed for both alloys, with the presence of coarse primary α-Mg grains, fine secondary α-Mg grains, β-phase, and other phases with a minor volume fraction. The amount of coarse primary α-Mg is significantly higher for the AZ91D compared with the MRI153M. The network of β-phase around the fine secondary α-Mg grains is better established in the thixomolded AZ91D alloy. A combination of several factors such as the ratio of primary to secondary α-Mg grains, localised corrosion or barrier effect due to other phases, as well as regions of preferential dissolution of the α-Mg due to chemical segregation, are thought to be responsible for the high corrosion resistance exhibited by the thixomolded AZ91D and MRI153M.

KW - AZ91D

KW - corrosion resistance

KW - hydrogen evolution

KW - magnesium alloys

KW - MRI153M

KW - thixomolding

KW - Engineering

UR - http://www.scopus.com/inward/record.url?scp=85078073566&partnerID=8YFLogxK

U2 - 10.1002/maco.201911327

DO - 10.1002/maco.201911327

M3 - Journal articles

AN - SCOPUS:85078073566

VL - 71

SP - 339

EP - 351

JO - Materials and Corrosion

JF - Materials and Corrosion

SN - 0947-5117

IS - 3

ER -