Alloys

Our range of alloys consists mainly of binary hyper-eutectic silicon-aluminium alloys (note: not AlSiC composites) where increasing silicon content results in lower expansion coefficients and increasing specific stiffness.

Osprey® controlled expansion (CE) alloys are suitable for a variety of applications where components are subjected to extreme temperature variations.

Main characteristics of Osprey® CE alloys

Controlled thermal expansivity: 5–17 ppm/°C
Low density: < 2.5 gm/cc
High thermal conductivity: 120–180 W/m K
High specific stiffness: 39 to 54 x103 Nm/g
Machinable, plateable, and weldable

Designation system for Osprey® CE alloys

The designations for CE alloys are constructed using the following model:

CE stands for Controlled Expansion.
The number following after 'CE' (e.g. 7 in CE7F) gives the room temperature CTE in ppm/°C.
The M grade alloys (CE17MF and CE13MF) contain small additions of iron (Fe), manganese (Mn) and magnesium (Mg) so that similar heat treatment to 6000 series alloys (Al-Si-Mg) produces hardening of the matrix.*

^{*Originally, this was to improve the machinability of the alloys but it can also be used to improve the strength, but at the expense of thermal conductivity.}

Range of alloys

The alloys below are part of our standard range. For mechanical and thermal properties for the alloys, consult the tables below this one.

Osprey® alloy	CTE, ppm/°C	Al/Si ratio, %
CE17F	17	73/27
CE17MF	17	73/27
CE15F*	15	65/35
CE13F	13	58/42
CE11F	11	50/50
CE9F	9	40/60
CE8F*	8	35/65
CE7F	7	30/70
CE6F	6	20/80
CE5F*	5	13/87

^{*Contact us for more data about this alloy}

Properties of Osprey® CE alloys

Mechanical properties

Mechanical properties (typical values)

	CE17F	CE17MF	CE13F	CE11F	CE9F	CE7F	CE6F
Composition	Al-27%Si	Al-27%Si	Al-42%Si	Al-50%Si	Si-40%Al	Si-30%Al	Si-20%Al
Tensile strength, ultimate	≥160	175-312¹⁾	205	193	181	≥100	N/A
Yield strength, MPa	100	282	147	189	-	-	N/A
Bend stgrength (thee point), MPa	-	-	300	300	300	270	319²⁾
Young's modulus, GPa	91.8	91.8³⁾	101.9	121.4	118	129.2	130
Rigidity modulus, GPa	35.8	35.8³⁾	42.2³⁾	48.6	46	51.6	N/A
Poisson's ratio	0.28	0.28³⁾	0.27³⁾	0.29	0.29	0.26	N/A
Density, g/cc	2.6	2.6	2.55	2.51	2.47	2.43	2.35³⁾
Hardness, HV	60	75-132¹⁾	90	-	230	-	N/A

^{1) Depending on heat-treatment condition}
^{2) Test pieces 4 mm x 3 mm x 40 mm}
^{3) Calculated values}

Thermal properties

Coefficient of thermal expansion, ppm/ºC (typical values)

	CE17F	CE17MF	CE13F	CE11F	CE9F	CE7F
Composition	Al-27%Si	Al-27%Si	Al-42%Si	Al-50%Si	Si-40%Al	Si-30%Al
100K-200K	-	-	-	7.8	-	-
200K-300K	-	-	-	10.6	-	-
100K-300K	-	-	-	9.2	-	-
-60–200ºC	-	-	-	11.6	-	7.6
Room temp.	15.3	15.3	12.2	11.4	9.1	7.2
25–200ºC	17.1	17.1	13.7	12.3	10.2	8.3
25–300ºC	18.1	18.1	14.6	12.9	10.9	8.8
25–400ºC	18.7	18.7	15.2	13.4	11.3	9.2
25–500ºC	19	19	15.5	13.7	11.4	9.7

Thermal conductivity W/m.K (typical values)

	CE17F	CE17MF	CE13F	CE11F	CE9F	CE7F
Composition	Al-27%Si	Al-27%Si	Al-42%Si	Al-50%Si	Si-40%Al	Si-30%Al
At -100ºC	-	-	-	-	-	180
At -50ºC	-	-	-	-	129²⁾	140
At -0ºC	-	-	-	-	-	135
At 25ºC	177.4	146.8	145	132	121	120
At 50ºC	-	-	-	-	-	110
At 100ºC	-	-	-	-	125*	110
At 200ºC	151.2	146.5	-	-	108*	100
At 300ºC	-	-	-	-	98*	88
At 400ºC	-	-	-	-	90*	80
At 500ºC	-	-	-	-	85*	75
Specific heat, J/kgºC	846.3	767.25	857*	754*	780*	785*

^{*Calculated values}

Microstructure

In the molten state Si and Al are mutually soluble, whereas in the rapidly solidified condition there is minimal solubility of Si in Al (< 0.3%) and even less solubility of Al in Si. The products are true alloys rather than metal-matrix composites (such as AlSiC) as all the phases present originate from an homogeneous melt.

The Al phase is continuous up to ~ 85%Al. Over approximately 40% Si, the Si phase also becomes continuous, offering a co-continuous duplex alloy (similar to AlBe alloys).

The continuous Si phase produces a stiff alloy with low thermal expansion and low internal stresses, whereas the continuous Al phase enhances thermal conductivity and toughness and lowers electrical resistance.

Consequently, as the Al content is increased, electrical conductivity, thermal conductivity, strength, toughness, CTE and machinability are also increased. For these reasons, it is best to choose the highest Al content alloy that is acceptable for the application.

Although Sandvik can supply machined components with Si contents as high as 85% Si (i.e. CE5F), the relative brittleness of this composition means whenever feasible it is often better to compromise on the exact expansion match required and use a lower Si content alloy. For example, Kovar®* packages (with a CTE of ~ 7ppm/°C) have been successfully replaced with CE9F, CE11F and even CE13F.

^{* Kovar is a trademark of Carpenter Technology Corporation}