Solidification Path of NemAlloy

Abstract

The use of aluminium castings in automotive industries has dramatically increased in the last few decades due to the beneficial effects that arise by combining light weight and mechanical properties. Many of these castings have been used as parts of diesel engine. Diesel engines are subjected to high thermo-mechanical stresses, especially in the combustion chamber area of their cylinder heads. Due to the increasing demands needed for high power engines, weight reduction and elevating thermal and mechanical loads current casting produced using standard aluminium alloys (family of Al-Si and Al-Si-Cu alloys) are already reaching their limits, especially at elevated temperatures (>250 °C). New aluminium alloys able to fulfill these customers’ demands are therefore needed. Recently, the NemAlloy (AlCu7MnZr) has been developed by the Nemak Linz R&D-Team for cylinder head production for high performance engines. Beside good mechanical properties at elevated temperatures, the new alloy offers: hot tearing resistance, high thermal conductivity, low thermal expansion, high thermal shock resistance, corrosion resistance and good suitability to massive production. In the present paper the precipitation sequences that take place during solidification of this alloy have been identified applying Thermal analysis technique. Thermal analysis has been successfully applied in aluminium foundries for characterization of aluminium cast alloys. Characteristic solidification temperatures (TLIQ, TDCP, \( {\text{T}}_{\text{Eu}}^{\text{AlSi}} \),\( {\text{T}}_{\text{Rig}} \), \( {\text{T}}_{\text{Eu}}^{\text{AlCu}} \), TSOL…) and fraction solid distribution have been collected to support simulation as well as to provide necessary data for process development. The solidification path of the NemAlloy (AlCu7MnZr) has been compared with the precipitation sequence observed during solidification of the standard AlSi7MgCu alloy currently applied for cylinder head production.