A novel Ni-free Zr-Cu-Ag-Al ((Zr48Cu36Ag8Al8)Si-0.75) and a Zr-Cu-Ni-Al ((Zr53Cu30Ni9Al8)Si-0.5) bulk metallic glass (BMG), for comparison, were employed for Nd:YAG laser spot welding with three pre-selected energy inputs, including a low (6.2 J), a medium (8.0 J) and a high (9.2 J) energy input. After the welding process, the microstructure evolution, glass-forming ability (GFA) and mechanical properties of the welded samples were determined by a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and the Vicker's microhardness test. The results showed the Zr-Cu-Ag-Al BMG has better weldability than the Zr-Cu-Ni-Al BMG. No crystallization was observed in the weld fusion zones (WFZs) or heat-affected zones (HAZs) of the welds under three pre-selected energy inputs. Therefore, the GFA indices of Delta T-x (Delta T-x = T-x - T-g, T-x is the crystallization temperature and T-g is the glass transition temperature), gamma (gamma = T-x/(T-g + T-I), T-I is the liquidus temperature) and gamma(m) (gamma(m) = (2T(x) - T-g)/T-I), and the mechanical properties of the Zr-Cu-Ag-Al BMG welds did not differ significantly in comparison to the parent material (PM). For Zr-Cu-Ni-Al BMG, HAZ crystallization was unavoidable when a lower energy input was used; therefore, the GFA indices and mechanical properties of the weld were affected. Furthermore, when the GFA indices, Delta T-x, gamma and gamma(m), were used to predict the thermal stability of the BMG HAZs, Delta T-x seemed to correspond more directly to the HAZ crystallization behaviors in this study. It was observed that the Delta T-x value of Zr-Cu-Ag-Al BMG was about 26% higher compared to that of Zr-Cu-Ni-Al BMG. (C) 2013 Elsevier B.V. All rights reserved.