Ultra-thin　plates　have　great　potential　for　applications　in　aircraft　skin,　the　packaging　industry,　and　packaging　of　electronic　products.　Herein,　1　mm-thick　5A06　Al　alloy　was　welded　with　friction　stir　welding.　The　microstructural　evolution　of　the　welds　was　investigated　in　detail　with　optical　microscopy,　scanning　electron　microscopy,　and　electron　backscatter　diffraction.　The　results　showed　that　the　friction　stir　welds　of　1　mm-thick　5A06　Al　alloy　were　well　formed　without　obvious　defect　and　with　a　minimum　thickness　reduction　of　0.025　mm.　Further,　the　grain　size　and　the　proportion　of　low-angle　grain　boundaries　decreased　with　decreasing　welding　speed,　because　of　the　increasing　degree　of　dynamic　recrystallization.　Among　all　of　the　welded　joints,　the　welding　speed　of　100　mm/min　yielded　the　smallest　grain　size　and　the　highest　proportion　of　high-angle　grain　boundaries,　and　thus　the　best　mechanical　properties.　Specifically,　the　tensile　strength　of　the　joint　was　greater　than　that　of　the　base　material,　while　the　elongation　reached　80.83%　of　the　base　material.