Environmentally friendly conversion treatmentsof magnesium alloys -- taking examples ofcorrosion protection and scrap recycling
Uan, Jun-Yen
National Chung Hsing University, Taichung, Taiwan
Email: jyuan@dragon.nchu.edu.tw1

2

Chemical conversion coating treatment/ energy-saving
Chromate [1]/ Cr6+ / Waste [2]Cerium [3]/ phosphate [4]/ Vanadate [5]/ stannate [6], etc/ Waste [2]corrosion resistance[1] M. M. Avedesian and H. Baker, ASM Specialty Handbook: Magnesium and Magnesium Alloys, ASM:InternationalMetals Park, OH., 1999.

Environmental friendly treatment / low pollution[2] J. E. Gray and B. Luan, Journal of Alloys and Compounds, 2002, 336, 88-113.

→carbonic acid solution[3] C. S. Lin and S. K. Fang, Journal of The Electrochemical Society, 2005, 152, B54-B59.
[4] H. Umehara, M. Takaya and S. Terauchi, Surface and Coatings Technology, 2003, 169-170, 666-669.
[5] J. L. Skar, L. K. Sivertsen and J. M. Oster, in ICEPAM – International Conference on Environmental friendly pretreatment for Aluminum and other Metals, Oslo, Norway, 2004, pp. pp. 1-4.
[6] M. A. Gonzalez-Nunez, C. A. Nunez-Lopez, P. Skeldon, G. E. Thompson, H. Karimzadeh, P. Lyon and T. E. Wilks,Corrosion Science, 1995, 37, 1763-1772.

Carbonic acid aqueous for conversion (hard)coating on Mg alloy / corrosion protection
J.K. Lin, K.L. Jeng and J.Y. Uan*, Corrosion Science, 53 (2011), pp.
3832-3839.
J.Y. Uan*, J.K. Lin and Y.S. Tung, Journal of Materials Chemistry, 20(2010), pp.761-766.
B.L. Yu, X.L. Pan and J.Y. Uan*, Corrosion Science, 52 (2010), pp. 18741878.
J.K. Lin and J.Y. Uan*, Corrosion Science, 51 (2009), pp. 1181-1188.
J.Y. Uan*, B.L. Yu and X.L. Pan, Metallurgical and Materials Transactions
A, 39A (2008), pp. 3233-3245.
J.K. Lin, C.L. Hsia and J.Y. Uan*, Scripta Materialia, 56 (2007), pp.
923-925.
3

CO2(g)

CO2(g) (recycled from industry)
Photosynthesis
Carbon being
immobilized on Mg alloy
Carbonfixationin nature
Hydrotalcite
layer on Mg
alloy
PH=4 H CO /HCO
23[Mg6Al2(OH)16CO3• 4H2O]

3O2(g)

HCO3-/CO32Mg alloy

Mg alloy
10µm

50µm

Photosynthesis is a process used by plant to convert light energy into chemicalenergy (sugars) which are synthesized from carbon dioxide and water.

Preparing aqueous carbonic acid (HCO3−/ CO32−)
CO2 into 3rd tank
CO2 into 2nd tank
CO2 into 1st tank

3rdtankCO22ndtank
CO2

5Compressor

1sttank
CO2

Aqueous HCO3-/CO32-

5

Carbonic acid aqueous (pH ~4) at 50 °C
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-

Away from sample
HCO3− + H+ (pH ~4)
Mg alloyalloy
Mg

Sample’s surface

Mg(Al) + 2H2O → Mg2+ (Al3+) + 2OH−+H26Mg alloy7

pH vs. percentage of CO32- / HCO3-Mg alloy

Mg alloy

8J.K. Lin, et al., Corrosion Science, 53 (2011),
9p. 3832.

Salt spray test (ASTM B117)
with layered double hydroxide coating

AZ91D Mg alloy substrate

0.5 cm2 hr conversion treatment / salt spary 36 hr / corro. spot <5 %0.5 hr conversion treatment / salt spary 12 hr / corro. spot <5 %J.K. Lin, et al, Scripta Materialia, 56, 2007, p.923.

.J.K. Lin et al., Corrosion Science, 51, 2009, p. 1181.

Carbonic acid conversion treatment / application examplesChemical conversion hard coating (CaCO3)
CO2
Mg, Al, Pb, Sr, Ba promote aragonite formation
Ca2+Ca2+2+CaMg alloy
Ca2+Ca2+CaCO3 layer
AZ91D

Ca2+CaCO3(s) + H2O(l) + CO2(g) = [Ca2+ + 2HCO3−] (aq)Mg + H2O = Mg2++ 2OH− + H2

13

14

1. Surface pH from acid to alkaline due to surf. corro.
in carbonic acid
2. Mg2+ promotes the coating of CaCO3
15

-0.8
-1.0E(VAg/AGcl)-1.2

die-cast AZ91D
LDH_5min
CaCo3_20min
CaCo3_25minCaCo3_30min

-1.4
-1.6
-1.8
-2.0

10-6

10-5

10-4

10-3

Current density(A/cm2)

10-2

10-1

17Environmentally treatments of Mg alloy scraps:
recycling and reuse
Song-Lin Li, Hung-Mao Lin and J.Y. Uan*, International Journal ofHydrogen Energy, 38 (2013), pp.13520-13528.
S.H. Yu, J.Y. Uan* and T.L. Hsu, International Journal of Hydrogen Energy,
37 (2012), pp. 3033-3040
J.Y. Uan*, S.H. Yu, M.C. Lin, L.F. Chen and H.I. Lin, International Journal ofHydrogen Energy, 34 (2009), pp. 6137-6142.
J.Y. Uan*, M.C. Lin, C.Y. Cho, K.T. Liu and H.I Lin, International Journalof Hydrogen Energy, 34 (2009), pp. 1677-1687.
J.Y. Uan*, C.Y. Cho and K.T. Liu, International Journal of Hydrogen Energy,32 (2007), pp. 2337-2343.
Y. F. Lung, Y.F. Syu, M.C. Lin and J.Y. Uan*,
Converting waste magnesium scrap into anion-sorptionable nanomaterials,
RSC Advances (2014), accepted.

18

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Post-consumer Mg scraps

Post-consumer Mg scrap
H2 generator

Low grade Mg scrap
Anion-sorptional mater. or catalyst
Currently, low-grade magnesium scraps andpost-consumer Mg alloys (e.g., coated (Cu, Ni)
magnesium) are not recycled.9
As an additive in aluminum alloys
As an desulfate agent in steel metallurgy
21

0.05

Semi solid560 ˚C

12.6 wt.% Al23

Stainless steel net

Mg/steel couple for H2 generation
AISI 304 S.S. net (cathode)

4 cm

4 cm
Front

Rear

Solidified Mg alloy (Mg scrap)

24

Hydrogen-on-demand
Fan

Fuel cell (8 W)

3.5% NaCl aqueous
26

(a)
(c)

H2 generation tank(b)LEDHydrogengenerationtank

100 W PEMFC Stack27

28

29

Mg alloy machining chip/scrap

Converting these fine flake Mg scraps into
anion-sorptionable nanomaterials
The nanomaterials, anion-exchangeablefilm on the flake surface, being able tofunction to take up most of the fluoride
and sulfate anions from waste water.

30

Chemical conversion in pH 1.5 NaCl aqueous at 25 °C

32

33

For AZ Mg alloys, carbonic acid is good for chemical
conversion coating treatment.
Ca2+/carbonic acid is good for conversion hard coatingwith CaCO3 film on AZ Mg alloys.
Post-consumer Mg scraps/ Hydrogen generator
Recycling fine flake-type Mg waste/anion-sorptionable thinfilm can directly form on the surface of the flake, the Mg
waste being able to function to take up fluoride and sulfate
anions from waste water.
34

3535

MetalCorrosion potential (volts) vs. SCE

Mg
Mg

-1.73
-1.73

Mg
Mg alloys
alloys

-1.67
-1.67

Zn
Zn

-1.05
-1.05

Mild
Mild steel,steel, Cd-plated
Cd-plated

-0.86
-0.86

Al
Al (99.99(99.99 %)
%)

-0.85
-0.85

Mild
Mild steelsteel

-0.78
-0.78

CastCast ironiron-0.73
-0.73

Pb
Pb-0.55-0.55

SnSn-0.50-0.50

StainlessStainless steel
steel 316
316-0.43-0.43

StainlessStainlesssteel
steel304
304
Stainlesssteel
304-0.38-0.38

Cu-0.22Ni-0.14

Au+0.18

Pt+0.88

ΔE = 1.29 V

ΔE = 2.55 V

R. S. Busk, “Magnesium products design”, Marcel Dekker Inc., New York (1987), p. 519.

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生命週期評估-盤查資料(Inventory analysis)

43
44-45

~8=X 5%X 5%Melging 800 W (2.2 Kg scraps), 2.2 hr, 6.34 MJ (1760 Wh) needed
6.34 (MJ)
2.2 (Kg Mg scraps)=A (MJ)

H2 produce electric power

1 (Kg Mg scraps)

44 D.L. Albright and J.O. Haagensen, IMA Annual World Conference, International Magnesium Association, Toronto, Canada (1997).
45 B. Kiefer, G. Deinzer, J.O. Haagensen and K. Saur, SAE paper no. 982225, (1997).
46 G. Deinzer, B. Kiefer, J.O. Haagensen and H. Westengen, in “Magnesium alloys and their applications”, edited by B.L. Mordike and K.U. Kainer,
Werkstoff-Informationsgesellschaft mbH, Germany (1998), pp. 119-124.

38 38

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CO2-2h/pH11.5-different temperature60ºC

50ºC

20µm

20µm

80ºC

70ºC

20µm

20µm

.Lin and Uan*, Corrosion Science, 51, 2009, p. 1181.40

Surface morphology / cross-section structure
CO2-2h/pH11.5-2h sample

50µm

10µm

epoxy
epoxy

5µm

AZ91D
AZ91D

20µm

41

Cl−

Cl−

Cl−−
Cl solution

Cl−

Cl−
Cl−

Cl−
Cl−

Cl−
Cl−

Cl−
Cl−

Cl−

Cl−

Cl−

Cl−−
Cl

Cl−

Cl−

Cl−

Cl−

Cl−

Cl2−−

CO3

CO32−

Cl−

Cl−

Cl−

Cl− −

Cl

CO32−

Cl− −

CO32−

Cl

Cl−

Cl−

Cl−

CO32−

CO32−

CO32−
CO32−
CO32− Cl− CO 2−
3
CO32−

Cl−

Cl−

Cl−
CO32−

Cl−CO32−

Cl−

CO32−
CO32−

CO32−

Cl− Cl−

Cl−

Cl−
Cl−
Cl−2−

CO3−2− Cl
Cl− CO3
Cl− Mg2+ Cl−
Cl− Mg2+ Cl−
Al3+ Cl−
Cl−Mg2+Cl−Cl−AZ91D Mg alloy

4242

EPMA-MappingCClCCl

hydrotalcitehydrotalcite insalt water (5 hr)
43

43

Layered double hydroxides structure (LDH)
Mg6Al2(OH)16CO3• 4H2O on Mg alloy

OH−Mg2+ or Al3+44

Mg-Al-F- LDH

Green Chemistry, 2001, 3, 257–260• novel solid base catalyst for C–C bondformation•. unprecedented catalytic activity in boththe important Knoevenagel and Michael
reactions46

Yu, Pan, and Uan*, Corrosion Science,52 (2010), pp. 1874-1878.

47

Mechanism

Bubbling Ar gas to remove CO32pH 6.8
CO2 -Free

Cl-Mg2+Al2+CO2 -Free

Al2+ Cl- Mg2+

ClClMg2+2+
AZ91D Mg Al3+
ClClAl2+
Cl22+ CO3 -Free
Mg
CO32- -Free 3+Al
pH~5.5pH 3.6

Deintercalation of Carbonate Ions:
Bubbling Ar gas

Remove CO3248