Onkelos the Convert is said by the Talmud to be the author of the official aramaic translation of the Pentateuch. Rashi and Maimonides understand Onkelos as having a tendency to interpret physical reference to God metaphorically. Indeed it seems very evident that throughout his work, Onkelos adopts this stance in his translation.
וַיּוֹצִאֵנוּ יְהוָה, מִמִּצְרַיִם, בְּיָד חֲזָקָה וּבִזְרֹעַ נְטוּיָה, וּבְמֹרָא גָּדֹל--וּבְאֹתוֹת, וּבְמֹפְתִים.
ואפקנא ה', ממצריים, ביד תקיפא ובדרע מרמם, ובחזוונא רבא--ובאתין, ובמופתין.
And the LORD brought us forth out of Egypt with a mighty hand, and with an outstretched arm, and with great terribleness, and with signs, and with wonders.
Onkelos translates hand and arm simply. He also does this in Exodus 13:14, And Deuteronomy 6:20, regarding hand. This is all in the context of the exodus, so their is a commonality as far as context. Why does he not use metaphor in this area? The only other use of arm that I am aware of in the Pentateuch is Deuteronomy 4:34, where it is translated the same way, in the same context. For hand, see Exodus 9:3, and 7:4, where Onkelos interprets hand to mean plague or strike.