Mechanical Properties and Quality in LPDC vs. CPC Casting

Mechanical Properties and Quality in LPDC vs. CPC Casting

• Tensile strength is comparable. Ultimate tensile strengths (UTS) differ by less than 7% between standard and low back-pressure CPC conditions. Both processes yield high-strength aluminum alloys.
• Microstructure remains consistent. Secondary Dendrite Arm Spacings (SDAS) show no measurable difference. Heat transfer during solidification is largely unaffected by back-pressure variations.
• Defect reduction is the CPC advantage. CPC applies 0.2-0.6 MPa during solidification. This continuous extrusion eliminates far-end shrinkage porosity in complex control arms.
• Oxide films limit fatigue life. Oxide bifilms are primary failure modes in tensile tests. CPC requires strict velocity limits to prevent oxide re-formation during riser tube movement.
• Hydrogen porosity is controlled. Hydrogen content stays near 0.16 ml/100g post-degassing. CPC's pressurized environment prevents hydrogen bubble expansion during solidification.
• Filling time requires adjustment. Higher back-pressure reduces venting rates. This causes a 12-second filling delay, necessitating adjusted pressure curves in CAE simulation.
• Thermal stress causes distortion. Fully coupled thermal-stress analysis is needed. This predicts distortion in H-shaped dies, ensuring dimensional accuracy for structural parts.
• Process stability ensures repeatability. In-die temperatures vary by less than 10 °C. Consistent thermal management guarantees uniform mechanical properties across production batches.

• Q: Is CPC stronger than LPDC?
  A: UTS differs by less than 7%; CPC's advantage is superior internal defect reduction.
• Q: Does back-pressure affect microstructure?
  A: No, SDAS shows no measurable difference between varying back-pressure conditions.
• Q: What causes failure in CPC castings?
  A: Oxide bifilms are the primary failure mode in tensile tests for CPC castings.
• Q: How does CPC prevent shrinkage?
  A: CPC applies continuous extrusion pressure during solidification to feed defects.
• Q: Why is filling slower in CPC?
  A: Higher back-pressure reduces venting rates, causing a 12-second filling delay.
• Q: What temperature variation is acceptable?
  A: In-die temperatures should vary by less than 10 °C for process stability.