Achievements and future challenges
in Magnesium Alloy Research andApplication in Australia
By Mark Easton
Mark Gibson, Suming Zhu, Trevor Abbott, Jian-Feng Nie, Gary
Savage, Carlos Cáceres, and many others

RMIT University©2012
University©2013

International
RMIT& Development
Engineering Portfolio

1Magnesium Research in Australia
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Australian	  Light	  Metals	  Ac1on	  Agenda	  in	  2001	  Originally	  developing	  a	  primary	  Mg	  smelter	  project	  in	  Australia	  –	  but	  cancelled	  in	  2004	  due	  to	  low	  metal	  prices	  Research	  Organiza1ons	  (all	  focused	  on	  light	  metals	  in	  general)	  ! CAST	  Co-­‐opera1ve	  Research	  Centre	  1993-­‐2013	  ! Industry	  engaged	  applied	  research	  ! CSIRO	  Light	  Metals	  Flagship	  2003-­‐2011	  ! Strategic	  research	  focused	  on	  step	  change	  industry	  opportuni1es	  ! Centre	  of	  Excellence	  in	  the	  Design	  of	  Light	  Metals	  2005-­‐2013	  ! Directed	  fundamental	  alloy	  design	  research	  Whilst	  these	  centers	  have	  been	  closed	  there	  is	  s1ll	  a	  strong	  legacy	  of	  capability	  and	  projects	  in	  Australia	  2

What is happening in the Mg world?
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Lots!!
Light weighting is definitely the issue of the moment, particularly in Europe but
also in North America (Ford F150 moving to an Al body structure)
Substantial interest/new orders for advanced Mg alloys from automotive OEMs

New smelter in Golmud,
Qinghua province
Electrolytic Mg (old Bécancour plant)
Magontec to produce 45ktonne
Mg alloys/year
Mostly hydro-power
6.5tonnes CO2/tonne Mg(compared with 25tonnesfor Pigeon process in China)

3Current Magnesium Research Projects
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LP130100828 High Performance Cast Magnesium Alloys! Understanding Mg-Al-RE alloys for higher strength-ductility combinations, forhigh temperature performance and improved castability (particularly YS)! CIs Easton (RMIT), StJohn, Nogita, Caceres (UQ), Chen (Monash), PIs
Abbott (Magontec), Schmid-Fetzer (Claustal), Gibson (CSIRO)
Commercial Research Project! Targeted alloy development in the Mg-Al-RE system for HPDC
! Funded by two European OEMs
Proposed Prototyping Project! Italian automotive component – using AM-SC1 to prototype an AE44 alloy inVictorian SMEs
Baosteel Australia joint research and Development Centre projects
predominantly at Monash University focusing on wrought alloys and coatings

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So what has happened to the technologies?
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AMCover (low GHG cover gas)
! Used quite widely in the industry. Patents dropped and little revenue could be generated from it.
Lots of GHG saved.
Alloys! AM-lite (Mg-Zn-Al alloys, decorative alloys): Magontec had a ZA128 alloy compared with theZA124 alloy from CAST. Best compromise around ZA126. Some small sales of alloys.
! AM-CAST (now called MicroZir, a Mg-Zr grain refiner): Magontec are now producing it and finding
a lot of interest in the market place.
! AM-SC1 (sand-cast creep resistant alloy): About to be used as a prototype for AE44
! AM-HP2/HP3/HP2plus (HPDC creep resistant alloys): Commercialization on hold. Performanceof alloys are beyond what is currently needed. Higher cost due to use of expensive REs (Nd, Y).
! AM-EX1 (extrusion alloy): Current development project with LKR. Commercial prospects unclear.
! Mg-Al-RE alloys (creep resistant/structural alloy): New provisional patent and focus on ongoing
research
Laser Assisted Self Piercing Riveting! Licensed to Henrob, a successful demonstration cell developed as part of the US-AMP program
Casting technologies (CSIRO)! Twin roll casting: still lots of interest in the market place but volumes are low! T-Mag (gravity tilt casting): spin off company
5Capabilities: Alloy Production! CSIRO and smaller scale at
University of Queensland! Two light alloy furnaces 30kg
Mg
! Heat treatment! Mg machining area
! Melt centrifuge! Cover gas! Spectrometer – calibrated forREs! J.Mat.Pro and Pandat Mg alloydatabase6

High Pressure Die Casting! CSIRO Clayton! Toshiba 250T cold chamberhigh pressure die castingmachine! Rauch Magnesium Mobile
Melter and Dosing Furnace! Casting Simulation Software:
MAGMAsoft, FLOW-3D,Calcosoft

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Property Testing! Hardness! Tensile! Creep (24 arms across CSIROand Monash)! Bolt Load Retention (UQ)
! Fatigue – stress and strain
controlled (CQU)! Some physical properties! Corrosion – Polarisation,Immersion, Salt spray, Outdoor
exposure (Monash, UQ, CQU)

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Microstructural Characterisation

Facilities across Monash, UQ, CSIRO, Deakin, RMIT! SEM – EDS, WDS, EBSD, FIB! TEM – including HR-TEM, Titan (Monash)! Atom Probe (x2 Monash)
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JoiningLaser Assisted
Self Piercing Riveting-licensed to Henrob

Without Laser

With Laser

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Magnesium Alloys and CAST!
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CAST Co-operative Research Centre
existed for over 20 years
A large effort into Magnesium Alloys
This presentation attempts to bring
together some of the major learnings
about magnesium alloys

Since CAST ended I have moved toRMIT University

AVL AM-SC1 crankcase

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Mg alloys – what have we learnt?
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Lots!!!

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Alloy systems investigated! Mg-Al: main commercial system AM50/60, AZ91
! Mg-Al-Sr,Ca,RE etc: some commercial alloys MRI alloys in particular,
AXJ530, AJ62 (BMW engine block) but little take-up!! Mg-Zn-Al(-Ca,RE) alloys such as AMlite
Lots!!!
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! Mg-Al-RE: current substantial growth and appear to be the alloys ofMg-Al: main commercial system AM50/60, AZ91!

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What makes a good commercial alloy?
Understanding
Hot tearing
Castability
Test methods
ModelsProcessing
Castability
hot tearing
fluidity

Cost fluctuations
Relating alloying
elements processing
and performance

PerformanceStrength-ductility
CreepCorrosion

Microstructure-propertyrelationships

Cost vs.
performance
Choice ofalloying elements
Cost13

Mg-Al alloys
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Most successful commercial system
Acceptable combination of strength, ductility and castability
AM50/60: Mg-(5-6)Al-0.3Mn! Higher energy absorption, castability more limited! Examples: Instrument panels, steering wheels, seats
AZ91: Mg-9Al-(0.5-1)Zn-0.3Mn! Excellent castability, good strength, ductility can be limiting in some applications! Housings, interior automotive components, electronic casings
Camera housing

Meridian IP beam (AM60)

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Mg-Al: castability!
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Mg-Al alloys become more castable with increasing
Al contentIncreasing Al content increases the amount of
eutectic and increasing fluidity and decreasing
feeding defects, e.g. hot tearing and porosity

K. Strobel, M.A. Easton, V. Tyagi, M.T. Murray, M.A. Gibson, G. Savage, and T. Abbott: Int. J. Cast
Met. Res., 2010. vol. 23(2), pp. 81-91.

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Mg-Al: strengthening (Cáceres, Dargsuch, Easton, Zhu, Gibson etc)

K.V. Yang, et al: Metall. Mater. Trans. A, 2014. vol. 45(9), pp.
4117-4128.

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Big steps in understanding strength, creep,corrosion, microstructure
We now know:! grain size and intermetallic volume andmorphology are critical to the strengthductility relationship! Corrosion is almost entirely dependent on
controlling the impurity levels! Increased Al in matrix is bad for creep but still
not completely sure why
150°C 50MPa 100 hrs

T.B. Abbott and M.A. Easton: Mater. Forum, 2001. vol. 25, pp. 181-201.

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Mg-Al: Importance of the skin (Caceres, Yang)
K.V. Yang, M.A. Easton, and C. Caceres: Mater. Sci. Engng. A, 2013. vol. 580, pp. 191-195.

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HPDC Mg alloys have a refined skinIts fine grain size is very important forstrengthening
Skin increases with solute content
Microplasticity approaches to the skin
Also affects creep properties (thinnersamples with increased proportion of skin)
150°C 50MPa

M. Dargusch, M.A. Easton, S.M. Zhu, and G. Wang: Mater. Sci. Engng. A, 2009.
vol. 523, pp. 282-288.

K.V. Yang, C.H. Cáceres, and M.A. Easton: Mater. Sci. Engng. A, 2013. vol. 580, pp. 355-361.

17Mg-Al: Problem of heat treatment (at least forHPDC)(Zhang, Easton, Zhu, Gibson, Savage)!
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AZ91 – no improvement in strength withheat treatment even T5
Main issue is grain growth (even in skinwith ageing and no solution treatment)
Also noticed that vacuum casting had only
!a small effect on the properties of the alloys

X.J. Wang, S.M. Zhu, M.A. Easton, M.A. Gibson, and G. Savage: Int. J. Cast Met. Res., 2014. vol. 27(3), pp. 161-166.

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Mg-0.65La

Mg-0.65La

Mg-0.47La-0.10Nd!

Mg-RE alloys (lowsolubility) showed asubstantial reduction
in strength withmorphology change in
the intermetallic after
heat treatment
B. Zhang, S. Gavras, A.V. Nagasekhar, C. Caceres, and M.A. Easton: Metall. Mater. Trans. A, 2014.
vol. 45(10), pp. 4386-4397
FEA modelingindicated this was dueto the break-up of theintermetallic network
Explains thedifference between
the predictions andmeasurements in MgAl alloys

Mg-0.45La-0.63Nd

Importance of the intermetallicnetwork (Zhang, Caceres et al)19Mg-Zn-Al alloys (Abbott, Nie, Easton, Savage)!
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Huge amount of interest and promise
Best overall castability of all the alloys that we havecast due to low temperature eutectic
However, this leads to too much brittle intermetallic andlimited ductility
Usable alloys can be found in the ZA12(4-8) range andare being used commercially (limited)Thin walled castings are where these alloys are best

Hot tear susceptibility

Easton, M.A., et al. in Magnesium Technology 2008. 2008. New Orleans LA: The Metals, Mineralsand Materials Society. p. 323-328.

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Tensile Properties from Die Cast Plates
AM-lite composition chosen to give best ZA alloy
ductility in thin sections

Tensile specimens cut from 2mm thick plate*% elong.

0.2% PSTSAZ91

1.8*155200AM-lite

3.0175245

ZA126

2.3183244

Hymag2

1.7191245

Average of 5, Stresses in MPa
Lower average ductility of AZ91
due to poorer filling of thin plate•ZA124 (AM-lite) gives good ductility
in thin sections but low resistance tohot tearing•ZA129 (Hymag2) has good
resistance to hot tearing but has lowductility•ZA126 a compromise between hottearing and brittleness limitations

21Mg-RE alloys (Gibson, Easton, Zhu, Nie,Abbott, etc)!
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Most studied system in CAST
Excellent/exceptional creep properties (better thanAluminium A380)
Cost-castability-creep-tensile properties
Getting the best combination of properties is not easytensileM.A. Easton, M.A. Gibson, S. Zhu, and T. Abbott: Metall.
Mater. Trans. A, 2014, in press.

creep

castability

S.M. Zhu, M.A. Gibson, M.A. Easton, and J.F. Nie: Scripta
Mater., 2010. vol. 63(7), pp. 698-703

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Designing a Mg-RE alloy (Gibson, Easton, Bettles)!
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AM-HP2plus has been found to be the optimum (Mg-La-Nd/Y-Zn-Al-Mn)
Start with a castable Mg-La alloy
Add RE elements that are soluble and precipitate and don’t affect the castability toomuch
Control the Al and Zn contents to optimize the creep properties of the alloys

èM.A. Gibson, M.A. Easton, V. Tyagi, M.T. Murray, and G.L. Dunlop, Further improvements in HPDC Mg alloys for powertrain applications, in Magnesium Technology 2008, M.O.
Pekguleryuz, et al., Editors. 2008, The Metals, Minerals and Materials Society: New Orleans, LA. pp. 227-232.

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Mg-Al-RE alloys!

Current Alloys – AE42 (some castabilityissues) and AE44 (excellent castabilityand properties but can they be improved?)

RMIT University©2013

RMIT Engineering24Mg-Al-RE alloys
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Higher strength – ductility combinations
than Mg-Al, particularly at higher
strengths
Could be best structural alloys
Eutectic is a fine fibrous type eutectic
rather than a divorced/semi-divorced
This could lead to the reinforcing by theintermetallic to increase strength without
the continuous fracture paths25Mg-Al-RE alloys!
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Good (but not best) creep resistanceReason for this still not completely clear
Latest results show these alloys dynamically
precipitate like other high creep resistantalloys, which contain Ca (MRI230D,AXJ530) or rare earths (HP2+)

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What makes a good alloy system?
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1. Good combination of castability and strength-ductility (essential requirement)! eutectic system with a non-continuous and well dispersed brittle phase is best (ductilephase is dominant in the eutectic)! This means that alloys can be made that are closer to the eutectic (good for castability)
2. Creep (for another talk in detail)! Grain boundary strengthening is important (but not that important)! Strengthening of matrix phase is important! Best creep resistant alloys contain soluble elements with low diffusivity (precipitation
during creep without overageing)
3. Corrosion (for another talk in detail)! Keep impurity levels low. Control with Mn! General corrosion of most of the ‘commercial alloys’ is sufficient! Galvanic corrosion is still the most critical issue! Coatings are important
4. Cost! Price stability and supply is as important as cost but don’t use too much expensive stuff27

www.rmit.edu.au/aeromecheng28