Citation: Maier, P.; Ginesta, D.;
Clausius, B.; Hort, N. Observations of
Microstructure-Oriented Crack
Growth in a Cast Mg-Al-Ba-Ca Alloy
under Tension, Compression and
Fatigue. Metals 2022, 12, 613.
https://doi.org/10.3390/
met12040613
Academic Editors: Menachem
Bamberger and Daolun Chen
Received: 26 February 2022
Accepted: 31 March 2022
Published: 2 April 2022
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metals
Article
Observations of Microstructure-Oriented Crack Growth
in a Cast Mg-Al-Ba-Ca Alloy under Tension,
Compression and Fatigue
Petra Maier
1,
* , Daniel Ginesta
1
, Benjamin Clausius
1
and Norbert Hort
2,3
1
School of Mechanical Engineering, University of Applied Sciences Stralsund, 18435 Stralsund, Germany;
daniel.m.roque@hochschule-stralsund.de (D.G.); benjamin.clausius@hochschule-stralsund.de (B.C.)
2
Functional Materials, Helmholtz-Zentrum Hereon, 21502 Geesthacht, Germany; norbert.hort@hereon.de
3
Institute of Product and Process Innovation, Leuphana University Lüneburg, 21335 Lüneburg, Germany
* Correspondence: petra.maier@hochschule-stralsund.de
Abstract: DieMag633, a cast Mg-Al-Ba-Ca alloy, was the focus of this study. Brittle interdendritic
phases strongly influenced the crack initiation and propagation under quasi-static and fatigue loading.
Especially under tensile loading, the material showed a low resistance to failure. Selected fatigue
loading sequences were applied to investigate their influence on crack propagation. DieMag633 in
this study contained shrinkage cavities and pores of significant size and irregular distribution. Even
though pores played a role in initiating the crack, it was mainly influenced by the Ba- and Ca-rich
phases, being and staying much harder under deformation than the Mg-matrix. Apart from the
fatigue crack propagation region under fatigue loading, there was no transgranular cracking found
within the dendritic α-Mg grains. Only under compression did the dendritic α-Mg grains bridge the
crack from one brittle phase to another. Transgranular cracking within the compact Ba-rich phase
was very pronounced, starting with many microcracks within this phase and then connecting to the
macrocrack. The lamellar Ca-rich phase showed also mainly transgranular cracking, but being small
lamellae, intergranular cracking was additionally found. The hardness increase under deformation
depended on the loading condition; a compression load strain-hardened the material the most. μCT
analysis was applied to characterize the amount and location of the shrinkage cavities and pores in
the individual gauge length.
Keywords: microstructure; crack propagation; brittle phases; porosity; fatigue; μ-CT analysis
1. Introduction
The die-cast Mg-Al-Ba-Ca alloy, called DieMag633, was developed as a creep resistant
alloy based on Mg-Al. Rare earths elements (REE) are often chosen as alloying elements
when a good creep resistance is desired in Mg-Al alloys. This is based on the formation
of precipitates like Al
11
RE
3
, Al
4
RE and Al
2
RE [1,2]. Alloying with Ba and Ca replaces the
expensive and limited REE, strengthening precipitates where expected. Based on AXJ520 [3]
and AX52/AX53 [4], where (Mg,Al)
2
Ca precipitates strengthen the alloys, and based on
Mg-Zn alloys, where alloying with Ba promotes both the formation of strengthening
precipitates by stimulating the precipitate nucleation and the acceleration of the kinetics of
precipitation during artificial and natural ageing [5], a Mg-Al-Ba-Ca alloy was developed
as a creep resistant alloy [6,7].
In this study the DieMag633 alloy, according to their alloying elements also known
as ABaX633, consists mainly of primary dendrites of α-Mg and two interdendritic phases
of different morphology. Increasing the amount of Al, Ca and Ba in the DieMag-series
(DieMag211, DieMag422 and DieMag633—numbers stand for amount of Al, Ca and Ba
in wt.%) increases strength and creep resistance based on the increasing amount of Al
2
Ca
and Mg
21
Al
3
Ba
2
[7]. In the study by Dieringa et al. [6] it can be seen that the DieMag422
Metals 2022, 12, 613. https://doi.org/10.3390/met12040613 https://www.mdpi.com/journal/metals