This paper presents the work of additive manufacturing (AM) of high strength aluminium alloys by the technology laser powder bed fusion of metal (LPB-L/M). LPB-L/B can enable great part design flexibility, and has very fast cooling rates which leads to very interesting As-built micro structure, often can give higher mechanical strength than conventional routes. This work aims to find suitable AM routes with LPB-L/M to enable the crack/defect free high strength Al alloys, in particular, AA7075 and part of AA6061. It is found that AM of AA7075 powder gave micro-cracks out of all tested 24 parameters. Introducing ZrH2 nano-particles by mechanical blending can successfully produce crack-free samples. Adding 5% Si into the AA7075 powder by mechanical blending can also give crack-free samples with very high relative density. We tested different preheating temperature for the AM process. Surprisingly found that, if with pre-heating at 200oC, the hardness in the as-printed state was as-low-as 70HV. Solutionizing at 480oC with water quenching followed with hardening at 120oC can bring the hardness to 140HV and 120HV, for AA7075 with ZrH2 and for AA7075 with addition of Si. The reason for the low hardness should be due to the in-situ over-aging of AA7075 alloys. It is concluded that preheating temperature should be carefully selected for AM of high strength Al alloys where the precipitation of small particles at the hardening mechanism.