As the standardization of fifth generation (5G) communications has been completed, and the 5G network will be commercially launched in 2020, the research visioning and planning of sixth generation (6G) communications are being initiated. 6G communications are expected to be the next focus in wireless communication and networking and aim to provide remarkable communication services to meet the future demands in the 2030s. We believe that the human-centric mobile communications will still be the most important application of 6G and 6G network should be human-centric. Following this rationale, high security, secrecy, and privacy are the all-important features of 6G, which shall be paid special attention from the wireless research community. To promote the research and the human-centric design ideology for 6G communications, we imagine in this article a comprehensive and systematic framework of 6G with five slices, key features, and enabling technologies. Furthermore, we briefly discuss the issues of 6G beyond communication technologies. Overall, the article aims to provide an envisioned picture of 6G and serve as a research guideline in the post-5G era.