Abstract: The microstructures of GH4720Li alloy samples which were cut from GH4720Li alloy bar including forging and heat treatment states were observed， and the phase compositions of primary γ′ was measured via energy spectrum analysis. The tensile properties of the samples through heat treatment were tested at 20 and 650℃. The results indicated that the quantity of primary γ′ of GH4720Li alloy decreases from the edge to the center of the bar while the size of primary γ′ increases gradually. The influence of heat treatment on the quantity and distribution of primary γ′ is not noticeable， but the influence of heat treatment on the quantity and distribution of secondary γ′ is noticeable. The tensile strength of GH4720Li alloy increases at the first and decreases in the end from the edge to the center of the bar， but the plasticity of alloy increases gradually. The quantity and plasticity of primary γ′ are the chief factors influencing the alloy plasticity. The phase boundary of primary γ′-γ is the crack source in the tensile tests. As the precipitation temperature rises， the plasticity of primary γ′ increase， the element contents of aluminum and titanium in the primary γ′ decrease， but the element contents of chromium， cobalt， molybdenum and tungsten in the primary γ′ increase.

Key words: GH4720Li, microstructure, mechanical property, γ′ phase, crack, composition segregation