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Abstract
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Ten-millimeter-thick strain-hardened AZ31B-H24 magnesium sheets were subjected to friction stir processing
(FSP) in air and submerged friction stir processing (SFSP) under water to investigate their
microstructures and microhardness properties. Different rotational speeds of 500, 630, 800, and 1000 rpm
and traverse speeds of 50, 100, 200, and 350 mm/min were employed for processing the materials. For
SFSPed samples, the rotational speed of 500 rpm and 200 mm/min of traverse speed resulted in an ultrafine-
grained structure with a minimum grain size of about 400-500 nm, which is half compared to that of
FSPed. It was found that both processes led to variation of crystallographic orientation, and enhancing the
rotational speed and lowering the traverse speed promoted the development of a {0002} basal texture. The
microhardness of SFSPed material increased significantly up to 110% ( 95 Hv), while the microhardness
was 45% ( 65 Hv) higher than the base metal ( 45 Hv) for FSPed material
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