DRSA Inreach Internal Stresses in Aluminum Engines Solidification
Feb 23, 2016
DRSA Inreach
Internal Stresses in Aluminum Engines
Solidification
Outline
• Introduction to solidification of casting alloys.
• Phase diagram for Al-Si.• Phases during cooling.• Different cooling rates throughout
cast engine head.
Phases
Melting and Boiling Temperatures
Simple systems have a melting temperature and a boiling temperature
Engines made from alloy of aluminum and silicon
More complicated in alloys
Phases
What is an alloy Not a compound◦H2O◦CH4
Mixture of two or more metals in any proportion
Aluminum too soft, weak Add silicon to harden and strengthen
Alloys
Aluminum and silicon come out of the melt and form separate components at the microscopic level
Rather than melting and boiling temperatures, look at Phase Diagrams
Alloys
Al-Si Phase Diagram
Al-Si Phase Diagram
Solidus
LiquidusEutectic
Microstructure Al-19%Si
Engine Head
◦Outside cools firstSolid outer shellMolten inner core, cools later, puts outer shell in tension
◦Different cooling rates lead to different microscopic structures◦Mismatch in microscopic structures create internal stresses
Internal Stresses
…Stresses and Strains
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