<p>Twin-roll casting (TRC) process is a high-efficiency and economical method for producing aluminum sheets directly from the melt. The microstructural characteristics and their formation mechanisms of 1070 aluminum alloy sheets produced by TRC were investigated, and the microstructures of this alloy were comprised of primary <i>α</i>-Al grains, iron-containing intermetallic compounds, and Al₉Si phase. The primary <i>α</i>-Al grains are relatively uniform in size along the width of the sheet, but there’s a noticeable difference between the outer zone and the central core. Grain sizes in the outer zone are 3–4 times larger than those observed in the central core. The size of Al₁₃Fe₄ phase located in the outer zone of the TRC sheet is smaller than that in the central core with much more scattered distribution, and the Al₉Si phase is a metastable intermetallic compound. It was analyzed that near-rapid cooling conditions essentially promote the formation of metastable Al₉Si phase, and the temperature gradient plays a crucial role in determining grain size and the distribution of second phases during the TRC process.</p>