CE alloy products - alloys and properties
Osprey CE alloys comprise a range of mainly binary hypereutectic silicon-aluminium alloys (note - not AlSiC composites) where increasing silicon content results in lower expansion coefficients (see the graph below) and increasing specific stiffness.
Standard range of controlled expansion alloys
Other alloys available are CE8F 8ppm/°C, CE13MF and development alloy CE5F 5ppm/°C.
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 CE7) gives the room temperature CTE in ppm/°C.
'F' is added to the alloy type (e.g. CE11F) to identify a finer grade than was previously available for CE alloys, that is a grade with a finer microstructure, which improves the strength and weldability of the alloy. As the finer grades have more consistent mechanical properties without reducing the thermal properties, the F grade alloys are now substituted for all the grades of CE alloys.
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
Mechanical properties for CE alloys
|Tensile strength, ultimate||≥160||175-3123)||205||193||181||≥100||N/A|
|Yield strength, MPa||100||282||147||189||-||-||N/A|
|Bend strength (three point), Mpa||-||-||300||300||300||270||3191)|
|Young's modulus, GPa||91.8||91.82)||101.9||121.4||118||129.2||130|
|Rigidity modulus, GPa||35.8||35.82)||42.22)||48.6||46||51.6||N/A|
1) Test pieces 4 mm x 3 mm x 40 mm
2) Calculated values
3) Depending on heat treatment condition
Thermal properties for CE alloys
|Specific heat, J/kgºC||846.3||767.25||857*||754*||780*||785*|
* Calculated values
Microstructure of CE alloys
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. CE5), 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 CE9, CE11 and even CE13.
* Kovar is a trademark of Carpenter Technology Corporation