MATERIALS I
LECTURE COURSE 10
ALUMINIUM AND ALUMINIUM-BASE ALLOYS
COPPER AND COPPER-BASE ALLOYS
OTHER NON-FERROUS ALLOY
ALUMINIUM
- Third widespread element (after O and Si)
- Most employed metal after Fe
- Extraction: from compounds (bauxite), finally electrolysis
Ex. Bayer method: bauxite >>> (refining) alumina
ALUMINIUM – Hall –Héroult process
Hot electrolysis: Al [cathode] + O [anode, reaction with C]
electrolyte: Na3AlF6
ALUMINIUM
Light metal – ρ = 2.7 x 103 kg/m3, IIIrd group
Tmelting = 660˚C, c.f.c. (a = 0.404 nm) without allotropic transformations
>>> very ductile
Very good conductor
electrical (after Ag, Cu, Au) ρel ≈ 0.23 μΩ m
thermal (after Ag, Cu, Au)
Impurities: Fe (Al3Fe at grain boundaries)
Si (as impurity, dissolved)
Mechanical properties:
E = 66 - 69 GPa; Rm = 50-180 MPa
(according to cold hardening degree and impurities amount)
ALUMINIUM – Young’s modulus
Maserati A6GCS/53 Pinin Farina
Steel tubular chassis (E = 210 GPa)
ALUMINIUM – Young’s modulus
ALUMINIUM AND ALUMINIUM-BASE ALLOYS
Mechanical properties depend upon purity
+ cold hardening degree
Purity State Rm min. A min.
[%] [MPa] [%]
99.997 Annealed 50 60
Cold 130 10
hardened
99.3 Annealed 80 42
Cold 180 5
hardened
ALUMINIUM – Corrosion resistance
High aphinity towards oxygen; forms amphoteric oxides
In atmosphere: completely protected by Al2O3 film
adherent/ impermeable/ chemically stable;
approx. 10 nm thickness
Resists: corrosive atmospheres, organic acids, water (sea also),
H2SO4 fumans !!!
Between 0-100˚C does nor corrode in water
(boehmit film = Al2O3 x H2O)
Above 100˚C thickness of boehmit increases
>>> peeling off (+ intergranular)
ATTENTION: electrolytic couple electrolitic with other metals!!!
Improvement: anodising – increases wear resistance also
ALUMINIUM – Anodising
ALUMINIUM – Soldering for avoiding
electrochemical corrosion
Al / Steel
ALUMINIUM
Engineering use (unalloyed)
- Cladding of less corrosion resistant alloys (duralumin);
- Chemical industry;
- Electric cables, foils, …
- Capacitor plates, telescope mirrors, …
CLADDED ALUMINIUM ALLOYS
Five-hundred-meter Aperture Spherical Telescope
(FAST) - China
ALUMINIUM BASED ALLOYS. CLASSES
According to the manufacturing method of parts
Foundry alloys
Wrought alloys not age-hardenable
age-hardenable
Foundry alloys: complex, highest amount / nr. of alloying elements
1 – cold forming; Form. Cast.
2 – hot forming;
ALUMINIUM AND ALUMINIUM-BASE ALLOYS
Foundry alloys
Good flowability and small solidification shrinkage
Best castability: Al – Si
Hypoeutectic alloys: α + E
Hypereutectic alloys: Si (very brittle) + E
Inoculation: fine eutectic structure
(fibres instead of lamellae)
Inoculant: Na (NaF, NaCl) – under 0.02%
Side - effect: eutectic at 13 – 14%
ALUMINIUM AND ALUMINIUM-BASE ALLOYS
Foundry alloys
Un-inoculated eutectic Alpax alloy Inoculated hypoeutectic Alpax alloy (9%Si)
12% Si: Rm = 180 – 200 MPa; A = 5 – 8 %
Through alloying (Cu, Mg), possibility for H.T:
Al-Si-Mg: Mg2Si and Al8Mg5 after H.T.
Ex. for auto / aero: 7%Si, 0.3%Mg, Al bal.:Rmmin=280MPa; Amin=10%;
Al – Si – Cu: Cu increases strength and machinability through H.T.
Decreases corrosion resistance!!!
ALUMINIUM AND ALUMINIUM-BASE ALLOYS
Foundry alloys
Al-Mg: low density, high corrosion resistance
Engineering alloys between 3 – 12%Mg, auto / aero
Advantages: Rmmax = 500 – 520MPa; Amax = 20 – 25%
Disadvantages: low castability, LONG HOMOGENIZATION!!!
Al-Zn: high corrosion resistance, good machinability
Applications: chemical industry (anodising also), hydraulics, …
Al-Cu: 4 – 14%Cu, not binary, generally (poor castability)
LOW CORROSION RESISTANCE!!!
Al-Cu-Mg: Ternary compounds that decrease hot strength (+Ni)
>>> Diesel pistons, air – cooled cylinder heads (old)
Al-Cu-Ni (Y alloys) – [Hiduminium Y]
Corrosion resistance+ hot strength >>> heavily loaded pistons
ALUMINIUM AND ALUMINIUM-BASE ALLOYS
wrought alloys
Non age-hardenable wrought alloys
Single-phased alloys (generally), with very good formability
(rolled profiles, extruded / deep drawn parts):
wrought aluminium
Al – Mn (max. 1.6%)
Al – Mg (max. 7%)
ALUMINIUM AND ALUMINIUM-BASE ALLOYS
Age – hardenable alloys
Alloys containing, in equilibrium conditions, secondary compounds
which dissolve in the solid solution when heated.
Double heat treatment:
1. Solution quenching (bringing the solid solution at room’s
temperature);
2. Aging (strengthening / hardening through the precipitation of out-of
equilibrium phases)
natural – at room’s temperature
artificial – through heating;
ALUMINIUM AND ALUMINIUM-BASE ALLOYS
Age – hardenable alloys
Duralumins – typical alloys
Al – Cu – Mg – Mn: 2 – 5.2% Cu; 0.2 – 1.8% Mg; 0.2 – 1.2% Mn
Effect of alloying elements:
Cu strengthening through HT
but diminishes corrosion resistance
Mg strengthening through HT
but lengthens homogenization duration
Mn removing the negative effect of Fe
ALUMINIUM AND ALUMINIUM-BASE ALLOYS
Age – hardenable alloys
For HT:
compounds that are soluble in α
Θ – Al2Cu
Phases with Mg
Through quenching: α structure
(maximum workability),
Stable in the first 2-3 hours
Al – Cu diagram
During aging, pre-precipitates (Guinier-Preston zones) are formed,
resulting in lattice stresses → strength / hardness
Through heating, stresses are lost (OVERAGING)
→ loosing of acquired strength / hardness
ALUMINIUM AND ALUMINIUM-BASE ALLOYS
Age – hardenable alloys
Analysis of aging: aging curves
Disadvantages of duralumins:
- Low corrosion resistance
(under stresses)
- Brittleness after welding
- High residual stresses after HT
Alloys which do not display
Aging curves for a typical Duralumin these drawbacks:
Al – Zn – Mg
Al – Mg – Si
ALUMINIUM AND ALUMINIUM-BASE ALLOYS
Standardization of aluminium alloys
SR EN 1780-1:2003 Aluminium And Aluminium Alloys - Designation Of
Alloyed Aluminium Ingots for Re-melting, Master Alloys And Castings
Part 1: Numerical Designation System
EN A B xxxxx
C
M
B – re-melting; C – cast parts; M – master alloy
First digit: 1 – un-alloyed Al; 2 – Cu; 4 – Si; 5 – Mg; 7 – Zn;
If first digit = 1: 2nd digit = 0; digits 3,4 = decimal fraction of Al content
For alloys: 2nd digit = group of alloys
Ex. 41xxx = Al-Si-Mg-Ti; 42xxx = AlSi7Mg; 43xxx = AlSi10Mg
3,4 digits – no special meaning
5th digit = 0 – general applications; ≠ 0 – special applications ingot
ALUMINIUM AND ALUMINIUM-BASE ALLOYS
Standardization of aluminium alloys
SR EN 573-1:2005 Aluminium and aluminium alloys - Chemical
composition and form of wrought products
Part 1: Numerical designation system
EN AW-xxxx (X)
First digit: 1 – un-alloyed Al (identical foundry al.); 2 – Cu; 3 – Mn; 4 –
Si; 5 – Mg; 6 – Mg si Si; 7 – Zn; 8 – other elements; 9 – unusual
classes
2nd digit: altering of alloy
For first digit =1 – altering in the limit of impurities / micro-alloying
Digits 3, 4 – no special meaning(not 1 series)
A, B, … - national variants
Ex. EN AW-5052; EN AW-5154 A
(SR EN 573/2:1995 Chemical symbol based designation system
SR EN 573/3:2004 Chemical composition)
ALUMINIUM AND ALUMINIUM-BASE ALLOYS
Standardization of aluminium alloys
SR EN 515:1994 Aluminium and aluminium alloys. Wrought products.
Temper designations
F – as fabricated
O – annealed to obtain lowest strength
H – cold hardened
H1, 2, 3, 4 x – cold hardened [+ bulk / surface treatment]
x – indicates the final cold hardening degree: 8 – hardest;
4 – ½ between O and Hx8
W – solution quenched
(only for naturally age-hardenable alloys)
T – heat treated to obtain stable tempers other than F, O and H
T1,2,3,4 – H.T with natural aging
T5,6,7,8 – H.T. with artificial aging
COPPER AND COPPER – BASE ALLOYS
Copper : reddish metal, very good thermal / electrical conductor,
very ductile
Density: 8950 kg/m3
Melting temperature: 1083°C
Crystalline system: f.c.c.
Very good conductor electrical (after Ag) ρel ≈ 0.015 μΩ m
thermal (after Ag)
Mechanical strength: 200 – 240 MPa
(annealed, according to the purity)
Corrosion resistance: good in atmosphere, water (sea also)
COPPER AND COPPER – BASE ALLOYS
Brasses = Cu – Zn alloys
Engineering brasses: max.45% Zn
Structure
α – up to 39% Zn
α + β’ – over 39% Zn (β’= solution / CuZn compound)
Good castability, very good formability (single phased)
Pb can be introduced for machinability
COPPER AND COPPER – BASE ALLOYS
Bronzes = alloys where copper prevails (excepting brasses)
Sn bronzes – oldest employed alloys
Engineering: max. 25% Sn
Structure α – up to 5-6% Sn - formable
α + (α +δ) – hard, wear resistant
Max. strength: 400 – 500 MPa
Corrosion resistance: good in water (sea also), neutral solutions
poor in HCl, HNO3
Al bronzes – Rm > 560 MPa, corrosion resistance > than Cu-Sn
Si bronzes – cheap, fluid, corrosion / erosion resistant
Be bronzes – Rm > 700 MPa, spark-proof, elastic
Standardization of Cu and Cu-base alloys
SR EN 1412: 1997 Copper and copper alloys.
European numbering system
[1 2 3 4 5 6]
1= C
2= B – re-melting ingot
C – cast product
F – filler for brazing / welding
M – master alloy
R – refined unwrought Cu
S – materials in the form of scrap
W – wrought products
X – non-standardised materials
3, 4, 5 = digits without a special meaning
Standardization of Cu and Cu-base alloys
6 = group of alloys
A, B – Engineering Cu
C, D – low-alloyed Cu (≤5%)
E, F – miscellaneous (≥5%)
G – Cu-Al alloys
H – Cu-Ni alloys
J – Cu-Ni-Zn alloys
K – Cu-Sn alloys
L, M – Cu-Zn alloys
N, P – Cu-Zn-Pb alloys
R, S – complex Cu-Zn alloys
Magnesium
Light metal: ρ = 1738 kg / m3
Tmelt. = 651˚C, h.c.p., no allotropic transformation;
Highly active chemically: reduces oxides / decomposes hydroxides /
carbonates of alkaline / metals / alkaline earth metals;
>>> air self ignite in aer in powder state (alloys also)
+ humidity / CH3CH2OH >>> explosive
Un-alloyed mechanical properties:
Rmax = 250 MPa (cold hardened)
A = 3 – 17 %
< 50 HB
E = 45 GPa
Magnesium – base alloys
Classes I. foundry
II. wrought
III. With special properties (applications)
I. Foundry alloys
a. High strength: Rm >300MPa dupa T.T.
b. Refractory: max. 400˚C (short time)
II. Wrought alloys
a. High strength : Rm > 340MPa, Mg-Al-Zn-Mn (Elektron)
b. Refractory : max. 250 – 300˚C for long duration
c. Super-light: Mg-Li (1140 – 1570 kg / m3) – satellites
III. Alloys with special applications
Ex. Ultrasound acoustic conductors
Glossary
• Aliaj neferos = nonferrous alloy;
• Aliaj de turnatorie / deformabil = foundry / wrought alloy;
• Aliaj care se durifica prin precipitare = age – hardenable alloy;
• Aluminiu tehnic = wrought aluminium;
• Duralumin = duralumin;
• Calire pt. punere in solutie = solution quenching;
• Imbatranire = aging;
• Prealiaj = master alloy;
• Alama = brass;
• Bronz = bronze;
