Autofill support Angular 6.0 with submit outside form html tag

I have a form in a component, and the submit button in another component wrapping the first one. Chrome/Firefox/Opera doesn't want to remember what user input in the form, how I can achieve that. Here, a simplified version of my html :

    <!-- First component -->
<form [formGroup]="_form" autocomplete="on">
            <fieldset formGroupName="identification">

                    <label for="immat">Numéro immatriculation *</label>
                    <input type="text" class="form-control" id="immat"
                        formControlName="numeroImmatriculation" name="lisaNumeroImmatriculation"
                        placeholder="Numéro d'immatriculation" autocomplete="on">                
<!-- second component, wraping the first one with ng-template, not shown here, containing the submit button -->
    <button type="submit" class="btn btn-primary navigation"