We propose a scheme to realize a topological superconductor and Majorana bound states (MBSs) in a one-dimensional metal nanowire on the surface of a helical altermagnet and in proximity to an $s$-wave superconductor, removing the requirement of conventional spin-orbit coupling and net magnetism. Through gauge transformation, we demonstrate that the helical frame naturally induces spin-momentum locking while the altermagnetism breaks time-reversal symmetry. The topological superconducting phase is well tuned by the chemical potential, altermagnet strength, and helical frequency. Furthermore, our transport calculation results reveal quantized conductance signatures: a $2e^2/h$ zero-bias peak at the nanowire ends and a $4e^2/h$ tunneling conductance at the domain wall of nanowires with opposite chirality, detected via a metal lead and scanning tunneling microscopy, respectively. Our research offers different perspectives on finding MBSs.

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• Majorana bound states
• 1-dimensional systems
• Altermagnets
• Topological superconductors
• Green's function methods