High temperature fatigue and creep – automotive power train application perspectives

Abstract

The present paper aims to describe the engineering durability design methodology as developed by BMW of hot power train components for both the gasoline cylinder head in aluminium alloys and the hot end components in iron based alloys under thermomechanical fatigue (TMF) conditions. The deformation is described using a viscoplastic model, which in the case for the aluminium alloys is combined with an aging model. The local damage evolution is modelled based on the growth of microcracks with a parameter derived from the J-Integral. Cyclic isothermal and non-isothermal fatigue tests were conducted in order to calibrate the lifetime model. The complexity was limited to a level that the main effects were captured but the analysis of a complex structure was still feasible. The accurate prediction of the variable temperature field is crucial for the success; in the CAE environment the temperature assessment remains the largest uncertainty. An outlook to new upcoming power train components is given.

Microstructure and mechanical behaviour of an elevated temperature Mg-rare earth based alloy

“…Each of these is challenging enough to achieve in isolation never mind in combination. Progress has been made, however, as demonstrated by BMW with its Mg/Al composite crankcase for an inline six cylinder engine, which uses an Al-alloy open deck insert and the Mg-alloy AJ62 for the outer shell [6,7]. The creep performance of the Mg-alloy was sacrificed in order to obtain the required level of die-castability necessary for the application.…”

TMF–LCF life assessment of a Lost Foam Casting A319 aluminum alloy

“…Engine efficiency, specific power increase and engine size reduction transformed the Thermo-Mechanical Fatigue (TMF) of the cylinder head fire deck into a critical design aspect in the automotive industry [1][2][3][4]. Therefore, the durability assessment of these components is increasingly in demand to ensure field reliability targets [5,6].…”

Characterization of intermetallics in Mg–Al–Sr AJ62 alloys

“…Therefore AJ62 is the only Mg-Al alloy so far that is used in mass production of an automotive power train crankcase, the BMW I6 Mg/Al composite crankcase [6][7][8] introduced in 2004. After development of the new AJ-alloys in 2003 research was done especially to determine the influence of alloy composition and microstructure on creep properties at high temperatures [1,9,10].…”