Specially　designed　Mg-Cu-Al　alloys　were　prepared　for　the　application　in　fracturing　balls.　In　comparison　to　Mg-2.5Cu　alloy,　Mg-2.5Cu-6.0Al　alloy　exhibits　an　improved　compressive　strength　of　378　MPa　and　compressive　strain　of　27%,　combined　with　a　high　degradation　rate　of　383　mm/y.　Two　kinds　of　second-phases　are　found　in　Mg-Cu-Al　alloys,　i.e.　MgAlCu　and　β-Mg17Al12+Al2Cu　phases.　They　form　a　discontinuous　network　and　act　as　cathodes　for　micro-galvanic　corrosion,　leading　to　a　high　degradation　rate.　Moreover,　the　addition　of　Al　could　improve　the　strength　and　ductility　simultaneously　in　Mg-Cu　alloys.　The　enhancement　of　strength　primarily　arises　from　the　solid-solution　strengthening　and　second-phase　hardening.　A　high　density　of　basal,　non-basal　dislocations　and　stacking　faults　were　activated　upon　mechanical　deformation.　This　accounts　for　the　good　ductility　in　Mg-Cu-Al　alloys.　©　2021