Refractory Metals for the Foundry Industry Application of Refractory Metals for Corrosion Problems High Corrosion Resistance A good corrosion resistance against molten metals is the prerequisite for a permanent application of die materials in the Foundry Industry. It has already been known for a long time that refractory metals and their alloys show an excellent corrosion resistance in comparison to hot working steel. New scientific investigations of the mass loss of refractory metals in molten aluminium confirm these facts (see graphic on the next page). Hence, the application of PLANSEE-Materials in critical areas of the die guarantees outstanding results: - Tungsten- and Molybdenum alloys are particularly suitable for the casting of aluminium and brass. Cores and die inserts due to their excellent corrosion resistance show a fundamentally higher tool life than any other conventional die material i.e. hot working steel. - An optimal surface quality of the casting can be achieved even after long tool life. Consequently the expenditure for cleaning and maintenance is considerably reduced. At the same time the low thermal expansion coefficient helps maintain tighter tolerances of the cast parts. - Cores and inserts from refractory metals reduce typical sticking effects of aluminium on the die surface, and therefore, reduce the amount of maintenance even further.
12
Embed
Refractory Metals for the Foundry Industry - Home | … · 2016-06-10 · Refractory Metals for the Foundry Industry ... Die insert for Al-HPDC process made of PLANSEE material ...
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Refractory Metals for the
Foundry Industry
Application of Refractory Metals for Corrosion Problems
High Corrosion Resistance
A good corrosion resistance against molten metals is the prerequisite for a permanent application of die materials in the Foundry
Industry. It has already been known for a long time that refractory metals and their alloys show an excellent corrosion resistance
in comparison to hot working steel. New scientific investigations of the mass loss of refractory metals in molten aluminium
confirm these facts (see graphic on the next page). Hence, the application of PLANSEE-Materials in critical areas of the die
guarantees outstanding results:
- Tungsten- and Molybdenum alloys are particularly suitable for the casting of aluminium and brass. Cores and die inserts due
to their excellent corrosion resistance show a fundamentally higher tool life than any other conventional die material i.e. hot
working steel.
- An optimal surface quality of the casting can be achieved even after long tool life. Consequently the expenditure for cleaning
and maintenance is considerably reduced. At the same time the low thermal expansion coefficient helps maintain tighter
tolerances of the cast parts.
- Cores and inserts from refractory metals reduce typical sticking effects of aluminium on the die surface, and therefore,
reduce the amount of maintenance even further.
2
Cross section of a D2M (Surface carborised) after 12,5 days in AlSi9Cu9 Melt Mass
loss <5%
Cross section of a TZM rod with TiB2 after 12,5 days in AlSi9Cu9 Melt Mass loss 1%
Cross section of a TZM rod after 12,5 days in AlSi9Cu9 Melt Mass loss 5%
- Due to the insolubility of Molybdenum and Tungsten in molten Aluminium compared to hot working Steel, inserts and cores
do not suffer from any erosion, which typically occurs when the parts are subjected to molten aluminium injected at high
velocities.
Filter Inserts Spreader for Al-Wheel Casting made of PLANSEE material
Graph 1: Mass loss of different materials in AlSi9Cu9 melt.
3
REM picture of a steel surface (1.2343) full with cracks due to thermal fatigue (heat
checking) after 45.000 cycles
- Dies, cores and inserts made of Tungsten and Molybde-
num alloys are very resistant to heat checking cracks as
the thermal expansion coefficient is 1/3 of Steel. As a result
the tool life is much longer.
- The application of PLANSEE materials eliminates the pro-
blem of heat checking cracks. The finished castings have
an optimal surface quality, which reduces the scrap rate as
well as maintenance requirements.
- The graph below (Graph 2) shows that the hardness of hot
working steel reduces dramatically after a certain number
of temperature cycles due to thermal fatigue. Although re-
fractory metals have a lower surface hardness initially, it
can be seen from the graph that the hardness stays the
same or even increases slightly.
Hence, the combination of high thermal conductivity and
low thermal expansion prevents the formation of heat che-
cking cracks.
Application for Heat Checking Problems
No Heat Checking Cracks
The die life, among other influences, is shortend by heat checking cracks (see picture below). This particularly applies to high pres-
sure die casting. The occurrence of heat checking cracks increases with an increasing temperature difference between the surface
layer and the underlying material layers as well as high thermal expansion and low hot strength of conventional die materials.
Tungsten and Molybdenum alloys have an excellent resistance to heat checking due to their low thermal expansion and good hot
strength at elevated temperatures. Additionally the high thermal conductivity guarantees a better temperature distribution and a
lower temperature difference between the surface and the core material layers (see Graph 2).
Graph 2: Maximum surface temperature versus energy input Graph 3: Surface hardness in Vickers versus temperature cycles
4
Improved Cooling Effect
In addition to their excellent corrosion and thermal fatigue
resistance, refractory metals have other physical and mecha-
nical properties that provide the die castor with completely
new opportunities for the die casting process. In case of fast
heat transfer requirements, Molybdenum and Tungsten al-
loys present excellent possibilities.
• In order to avoid shrinkage porosity in hot spots of the cas-
ting, a sufficient cooling effect must be ensured. The ther-
mal conductivity of Tungsten and Molybdenum alloys is 3
- 5 times higher than that of conventional die materials. This
offers a distinct higher cooling potential (see pictures on the
right).
• The application of these materials can be used to influence
the quality of the castings i.e. improve the mechanical pro-
perties by reducing the DAS (Dendrite Arm Spacing).
• In some cases complicated, maintenance intensive cooling
systems can be eliminated since the heat can be dissipated
sufficiently with refractory metals.
• The high thermal conductivity can also be used to reduce
the cycle time of some casting processes.
Cou
rtesy
of T
CG
UN
ITE
CH
AG
Die insert for Al-HPDC process made of PLANSEE material
Die insert for Al-Wheel Casting made of PLANSEE material Core pin for Al-HPDC process made of PLANSEE material
Application for Shrinkage Porosity Problems
D185 combustion chamber die inserts
Surface temperature of the die
with hot working steel core pins upon opening
Surface temperature of the die
with one TZM core pin upon opening
5
Mechanical and Physical Properties of PLANSEE-Materi-als in Comparsion with H13 (1.2343) Hot Working Steel
Properties
Mo TZM D2M D176 D185 1.2343
Corrosion ++ ++ + + + --
Oxidation from 400 °C from 400 °C from 600 °C from 600 °C from 600 °C no problem