ABSTRACT:

In the present study, rotary friction welding is used to fabricate welded joints from two different type of material, a medium car bon steel grade AISI 1045 and aluminum alloy AA 7075. Rods of 16 mm diameter 100 mm long from the two materials have been prepared for friction welding under two different conditions.  The medium carbon steel have been supplied in the cold rolled condition and annealed condition. The welding parameters for the cold rolled condition  was 1600 rpm of rotational speed, 14 MPa of friction pressure, 29 MPa of forging pressure, 66 sec of friction time and 2 sec of forging time. After welding, the samples were hardened for improving the mechanical properties. While for the annealed  condition, the welding parameters were 1080 rpm of rotational speed, 13 MPa of frictional pressure, 25 MPa of forging pressure, 63 sec of frictional time and 2 sec of forging time, after that the welds hardened and tempered  and prepared  for the microstructure examination, hardness test, tensile test and fatigue testing.

Experimental results showed that the microstructure of the WZ consist of Widmanstatten ferrite gathering on the boundary of pearlite, and the grain structure of the HAZ have finer size than the BM zone, due to action of heat generation, and the hardness at WZ showed the maximum value due to high amount of heat which produces  Martensite during cooling phase in these alloys, but after hardening, the hardness at WZ, HAZ and BM zone have the same magnitude.

Joint efficiency of first condition in tensile test and in fatigue test was about 100% in the hardened condition.  In addition, joint efficiency of second condition in tensile test and in fatigue test was 103% after hardening treatment.

On the other hand, aluminum alloy AA 7075 was used in two different conditions, in the T6 condition and annealed AA 7075. The parameter of friction welding used was 1600 rpm of rotational speed, 8 MPa of frictional pressure, 16 MPa of forging pressure, 60 sec of frictional time, and 2 second of forging time for both conditions.

Macro examination of full sections of the weldments showed linear defect at the weld zone interface due to high thermal conductivity and copper content of aluminum alloy AA 7075. The hardness profile across the weld zone showed high magnitude because of artificially aging produce GP zones, but at the HAZ have lower hardness due to complete dissolution of the low temperature precipitates like the coherent GP zones, and partial dissolution and coarsening of existing high temperature precipitates, like over aging of the semicoherant of the GP zones.  The welded joint was not good enough and the joint efficiency was about 16% in both the tensile test and the fatigue test.

 

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