Randschichtlegieren von AlSi8Cu3-Zylinderkurbelgehäusen mit Silizium mittels Diodenlaser

The suitability of the new process in principle has been confirmed. For that reason, at present a pilot unit is being built at Hydro Aluminium Deutschland according to this concept to test suitability for mass production.The following technological and scientific questions still remain to be classified. 1. Influence of pre-heating temperature on alloying depth, silicon precipitation and internal stresses in the aluminium and silicon. The aim is to determine an optimum process temperature for the edge-layer alloying of cylinder crankcases under the boundary conditions of optimum structure and minimised internal stresses in the layer [15]. 2. Theoretical estimates indicate the potential for considerable optimisation in the alloying of preheated cylinder crankcases. Calculations have shown that at a temperature of 200°C the intensity of 500 W/mm 2 can be reduced to 360 W/mm 2 . Using a 6 kW diode laser, this allows the focal point to be enlarged from the present 10 mm to 14 mm, giving the possibility of increasing the displacement between tracks from 4 to 6 mm and so reducing the process time per lining by 33% from the present 175's to 117 s. This would improve the process economy by 50%. First experiments have shown that the cooling circuit built into the crankcase can be used successfully to maintain the correct working temperature. 3. Further potential for optimisation is given by the coupling of 4 diode lasers each with an initial power of3 kW, so that 12 kW are available on a focal width of 20 mm. The displacement between tracks could then be increased from 4 to 9 mm and process time per lining reduced from 175 to 78 s. If in addition the processing temperature of the crankcase is 200°C, the intensity required could be reduced and the focus enlarged to over 30 mm. Then, the processing time for alloying a lining with 12 kWand a temperature of 200°C would be less than one minute, making the process competitive in relation to alternative methods.