Design
The N52 engine block is cast with magnesium and aluminum for the crankcase. Magnesium is used to save weight, however magnesium is subject to a greater risk of corrosion from water. However, magnesium may tend to creep under load at high temperatures. Thus, magnesium in its pure form or as a conventional alloy is not suited for permanently conveying high loads and forces of the kind typically encountered in central components of the engine. Therefore, BMW combined the N52 block to use magnesium alloy for the crankcase shell, with an aluminum “inner block” to complement the magnesium disadvantages.
For the cylinder liners the N52 Engine uses Alusil to coat the aluminum cylinder sleeves. Alusil is an aluminium alloy commonly used to make linerless aluminium alloy engine blocks. Alusil, when etched, will expose a very hard silicon precipitate. BMW switched from Nikasil-coated cylinder walls to Alusil in 1996 to eliminate the corrosion problems caused through the use of petrol or gasoline containing sulphur.
Read more about this topic: BMW N52
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