Influence of Microstructure on Corrosion of As‐cast ZE41

Abstract

Magnesium alloys are the lightest structural materials and have great potential in the automotive, aerospace and electronic industries in which weight reduction is a necessary requirement. [1][2][3] Among the most common commercial magnesium alloys, those containing rare earth (RE) elements are highly attractive due to their good strength and ductility. In particular, some exhibit high specific strength and good creep resistance at elevated temperatures. [4][5][6][7][8][9] ZE41 is one of the most popular magnesium alloys in the Mg-Zn-RE alloy system and has been widely used in the as-cast condition. For example, the gear case in the French Freron super helicopter is manufactured from as-cast ZE41 [10] as were the wheels [11] of the champion racing car in the years of 1990 and 1991.A significant limitation for the potential use of magnesium alloys is their susceptibility to corrosion. [12][13][14][15][16] Corrosion restricts their potential application. An important issue for magnesium alloys is to understand the factors that influence corrosion and therefore to understand the necessary conditions to achieve good corrosion resistance. Many intensive fundamental investigations into the corrosion behavior of magnesium alloys have been carried out during the past decade. The microstructure should be an important factor controlling the corrosion behaviour. [20][21][22]26,[35][36][37] However, there is little reported in the literature on the role of microstructure on the corrosion behavior of ZE41. The influence of microstructure on corrosion for as-cast ZE41 is still an open issue. Wide industrial production and engineering application of ZE41 require an understanding of its corrosion behavior and how the behavior is influenced by its microstructure. This research aims to clarify the influence of the microstructure on the corrosion of as-cast ZE41. The corrosion behavior of as-cast ZE41 is also compared with that of pure Mg and AZ91D, the most popular Mg-Al alloy. Experimental ProcedureSpecimens were cut from an as-cast ingot of ZE41 with nominal composition (in wt%) Mg 4 %Zn 1 %RE. The actual composition was 4.59 %Zn, 1.05 %Ce, 0.48 %La, 0.02 %Mn, 0.004 %Al, 0.006 %Fe, < 0.001 %Ni, < 0.001 %Cr, < 0.002 %Cu, < 0.002 %Zr. The compositions of the comparison alloys were as follows: (i) pure Mg had the composition of 99.94 wt%Mg, 0.014 %Si, 0.0086 %Mn, 0.0045 %Fe, 0.00092 %Ni, and 0.0066 %Al and (ii) AZ91D had the nominal composition of 9 %Al and 1 %Zn remainder Mg, and actual composition 8.26 %Al, 0.69 %Zn, 0.14 %Mn, < 0.002 %Fe, 0.002 %Ni, < 0.001 %Cr, < 0.002 %Cu, < 0.002 %Zr. All three alloys can be considered to be high purity because they all contain low levels of the impurity alloys Fe, Ni and Cu and thus the pure Mg and AZ91D used in the present study should be directly comparable with those used in prior studies. [20,23] The ZE41 had a slightly higher Fe concentration. The microstructure of ZE41 was examined using optical microscopy and scanning electron microscopy (SEM) after metallographic preparation (mechan...

Influence of fine‐grained structure produced by groove pressing on the properties of pure Mg and commercial ZE41 alloy

“…In ZE41 alloy, in addition to the Mg peak, some peaks of T‐phase (Mg 7 Zn 3 RE) are also observed and is confirmed by comparing with the published data 17,28,29 . However, some researchers also reported the presence of the peaks for Mg 12 RE phase in ZE41 alloy 30,31 . This phase was not observed in this study.…”

Magnesium Corrosion in Different Solutions

“…The corrosion rate at steady state gave the following alloy ranking: HP Mg~AZ91~ZE41 < Mg2Zn0.2Mn, although the corrosion rate of Mg2Zn0.2Mn was only slightly greater than that of the other materials. Table 2 presents the corrosion rates in the 3% NaCl solution at steady state, and evaluated as an average value over 120 and 240 h. These values of the corrosion rates for HP Mg, ZE41 and AZ91 agree well with prior measurements [6,11,12] giving confidence in the measurements carried out in this work. Corrosion rates at steady state give the following alloy ranking: HP Mg < Mg2Zn0.2Mn < ZE41 < AZ91.…”

Review of Recent Developments in the Field of Magnesium Corrosion

“…The corrosion rate was essentially independent of immersion time, and was ≈0.3 mm y −1 . That corrosion of high‐purity Mg is independent of immersion time is consistent with the literature . There were some specimens with higher corrosion rates.…”