Ultrafine grained AA1050/AA6061 composite produced by accumulative roll bonding
In this work accumulative roll bonding (ARB) was used to combine AA1050 and AA6061 sheets to produce an AA1050/AA6061 composite sheet with ultrafine grained (UFG) structure. Two different starting materials were roll bonded as alternate layers up to 5 rolling cycles with 200 degrees celcius pre-heating for 3. min before each cycle. Other two types of the UFG sheets with monotonic starting materials, AA1050/AA1050 and AA6061/AA6061, were fabricated by the same ARB process for comparison. The AA1050/AA6061 composite sheets with strong bonding between different materials were obtained and substantial grain refinement was achieved after ARB processing. It was found that two different materials in the AA1050/AA6061 composite deformed in a nearly identical way during the first 3 ARB cycles. Afterwards the AA6061 started to neck and eventually fractured. The areas around the interface of two different materials were observed by transmission electron microscopy (TEM) and it was found that the microstructure of the bonded interface was quite complex. Two types of interfacial morphologies were observed along the AA1050/AA6061 interfaces: Type I is the area with direct contact of fresh metals and type II is the area with original metals with surface brittle layers in between. The rule of mixture has been applied to predict the strength of the AA1050/AA6061 composite sheet using the mechanical properties of the AA1050/AA1050 and AA6061/AA6061 sheets. The predicted and the measured tensile strength values are comparable to each other. The hardness values of the AA1050 and AA6061 layers in the composite are close to those measured in the monotonic material laminates, which indicated that both materials accumulated similar strain no matter if they are deformed in the composite sheets or in the single material sheets.
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