Abstract
The 6000 series aluminum alloys and its composites welded joints suffer from solidification cracking and loss of strength in their fusion zone. Formation of fine equiaxed grains in weld fusion zones is considered one of the best solutions to avoid such problems. AA 6028 aluminum alloy and its nanocomposite (reinforced with 2 mass% Al2O3) have been gas-tungsten arc welded with different four filler metals. The first one was Al-12%Si piston alloy. The second, third and fourth ones are Al-6% Si-based reinforced with TiB2 and Al3Ti nano-constituents produced from addition of Al-Ti5-BI master alloy with different percentages (1, 2, and 3%). The microstructures of the base and weld zones were investigated using optical microscope and scanning electron microscope equipped with EDX analyzer. Microhardness of the base material and the weld zone were evaluated using a microhardness tester. All the weld joints were successfully welded without any cracks, large pores or solidification cracks. In case of Al-12%Si piston alloy filler metal, the weld metal shows fine dendritic eutectic structure for the AA 6028 alloy and its nanocomposites base metals. The hardness of the weld zone was increased almost as twice as the base metals. For the filler metals that treated with Al-Ti5-B1 master alloy, the weld zone structure shows fine dendrite eutectic morphology structure inside alpha - Al grains in addition to TiB2 and TiAl3 precipitates distributed within the weld zone of the AA 6028 base metal. In case of the nanocomposite base metal, the weld metal was consisted of fine and equiaxed grains with modified eutectic structure and reinforced with TiB2 precipitates and in-situ TiAl3. The hardness distributions inside the weld zone were almost homogenously as high as twice as the base metal. As the amount of Al-Ti5-B1 master alloy increased in the filler metal, the hardness will increased.